Last night I was at LBi in the old Truman Brewery on London's Brick Lane for Mashup's Location ... It's Moving On. I've spoken at a Mashup event once or twice before but this time the organising team threw caution to the wind and asked me to chair the panel discussion.

Prior to kicking the panel discussion off, I attempted to gently suggest some topics to my fellow panelists that we might want to discuss.

We started off with a quick review of my Theory of Stuff and how it applies to deriving value from location and location data and briefly visited Gartner's hype curve which puts location based services on the so called Plateau of Productivity. This is a good thing apparently. I then presented the panel with a series of  "yes, but" style trade offs to mull over.

• Smartphones vs. other phones; 21% of phones expected to have GPS by EOY 2009, but what about the other 79% without?
• LBS and LBMS vs. other (older) location systems (APIs and so on); LBS and LBS apps get all the publicity but what about key location APIs, platforms and services?
• "where's my friends" vs. creating value and creating data; "where's my friends" doesn't work as a (sole) business proposition but creating value added data does -- FourSquare and Gowalla are creating geotagged local business listings from check ins.
• "where's my business" vs. location based advertising; Tesco and Starbucks are the latest companies to launch apps to drive customers to their premises, but what's needed to drive location based ads?
• "where I think you are" vs. "where I say I am"; For a user, being able to be their own source of truth is imperative, but how can you reconcile this with your business needs?
• "where you are" vs. "where you've been"; (AKA tracking vs. privacy) How to walk the fine line between providing enhanced relevance via a user's location and being accused of tracking them.

I recently wrote about echoecho, an SMS based location sharing service and rather dismissed it as another PlayTxt or DodgeBall, both of which are now shuttered, and argued that EchoEcho fails my Theory of Stuff.

Nick Bicanic, the CEO of Purpose Wireless, the company behind echoecho was good enough to look me up and drop me a long email commenting on my blog post and -- very politely -- pointed out that I might want to revisit my opinion of the service. An edited version of that email to me formed the basis of his latest blog post on the topic of location as a context.

Like a lot of people, I get most of the information I use, both personally and professionally, from the web; from RSS feeds, from keyword search alerts and from Twitter. The genesis of my recent Theory of Stuff slowly accumulated out of this mishmash of feeds, alerts and status updates.

Firstly I read about EchoEcho, a new location based service which promises all manner of good stuff by showing you where your friends are regardless of which location based service they currently use. Let's leave aside for one moment that the service independence of this app seems to be based around the concept of getting all your friends to use EchoEcho and then consistently getting them to report their location. Let's look at something far more fundamental than that, the strong sense of location deja vu harking back over two years ago. Haven't we been here before?

Whenever I talk about the privacy implications inherent in sharing your location with an app or service, I keep coming back to the idea that it's essential to be your own source of truth for your location. This is a slightly verbose way of saying that you need to be able to lie about your location or that you need to be able to say "no, I really am here" despite what other location contexts such as GPS, cell tower triangulation or public wifi MAC address triangulation may have to say on the matter.

Of course, it's never quite as straightforward as that and here's why. The two location based mobile services that are getting a lot of coverage at the moment are FourSquare and Gowalla.

We all suffer from SPAM, the unwanted and unsolicited commercial bulk emails that are the reason we have Junk Mail filters and folders in our email clients and servers. A quick glance at the Junk folder for my personal email account shows over 300 of these since the beginning of February alone. If you use some form of instant messenger, be it MSN, Yahoo!, ICQ, AOL or any of the others on the market, you've probably come across SPIM, Instant Messaging SPAM. Then there's also mobile phone SPAM via text messages, comment SPAM, the list goes on and on.

We're poised to start seeing a new form of SPAM raise its ugly head. Let's call it LAMB for now, Location Based Advertising SPAM.

As Ed Parsons pointed out on his blog yesterday, Apple are banning location based advertising in apps. "If you build your application with features based on a user’s location, make sure these features provide beneficial information. If your app uses location-based information primarily to enable mobile advertisers to deliver targeted ads based on a user’s location, your app will be returned to you by the App Store Review Team for modification before it can be posted to the App Store."

This is a good first step in locking down potential abuses of a technology before it has a chance to get out of control. The reason we have SPAM and all the other variants in the first place is that the underlying technologies were designed in an open manner with no control mechanisms in place to thwart unsolicited and unwanted messages and content. But we need to go further than this.

Once again, this is not the post I set out to write. The one I set out to write was called "In Search of Location's Sweet Spot" and it's sitting in draft and not yet posted. That's because before I can submit that post I need to write this one as a warm up act. Just like Anne Elk (Miss), I have a theory. I call it my Theory of Stuff. I'm sure that other people, far more learned and erudite than I, have articulated such a theory but I've yet to come across any evidence for this and for now at least, it remains mine and it contains three buckets, looking something like this:

With the Yahoo! Geo Technologies sponsored, London #geomob meetup coming up this week, this weekend I took a look at how many companies were actively using location within London. No easy task. After much web searching this weekend I took a trawl through those companies tagged as being in London in CrunchBase, the database of tech companies that TechCrunch operates.

Not strictly scientific but then again this is more about gauging a trend than being strictly empirical.