I wrote a web app in Rails for collecting system statistics from Sparkle, I figured you might be interested in using it for Textmate since you also use Sparkle for updates. It's self-hosted, so you need a server and some basic admin skills.

Here's the project: https://github.com/mackuba/sparkler

And here's what kind of statistics it can generate: http://sparkle.psionides.eu/feeds/gitifier/statistics (this is data from 4 years back as you can see, so it will take a while for it to look like this :)

Let me know if you decide to use it and manage to set it up, I'll link to you from the readme. Also let me know if you run into any problems, I don't know if those instructions are intuitive enough.

Kuba