The AppleSeed testing program for 10.6 Snow Leopard (SL) officially closed at 0:00 today, so I am finally free of the Non Disclosure Agreement I signed, and can talk about the testing I did. I was fortunate enough to be able to test 6 builds of 10.6, and can say it's come a long way since it was first previewed at the Apple's WWDC in June.

It was really funny to read a lot of the speculation around the web about what would and wouldn't be in SL as I watched it evolve in the different builds. For example, there was a lot of hype about "Dock Exposé" or "Dockposé" which was demonstrated first at the WWDC, yet wasn't included in the build distributed to developers at the WWDC (10A380). It actually didn't make it in until 3 builds before SL went gold.
I think the product that is shipping today is excellent for what it's intended to be, but if consumers are expecting something like the transition from Tiger to Leopard, they will be very very sorely disappointed. Consumers need to understand that 10.6 paves the way for some great things down the line, but the changes are mostly invisible to the end user. Specifically, in my view SL has 3 main goals:

1. Increase speed and stability of the OS (lower memory usage, apps re-written in 64 bit, cocoa Finder, etc)
2. Take advantage of multi-core CPUs better (i.e. through GrandCentral)
3. Reduce size of the OS (better for portables)

SL sees a large size reduction due to dropping the PPC architecture support, and including far fewer printer drivers by default. This makes it better suited for a wider range of devices with limited storage, like the Mac Tablet (Newton?) which will supposedly drop in September. Users looking to further reduce the OS footprint should look into apps like Delocalizer (free) or XSlimmer ($14.95US).
Some other things I like:

• Cocoa Finder is an awesome improvement. Much faster and more responsive, and handles connections to shared servers much better.
• OpenCL rendering is great. Much faster previews of PDFs, etc.
• Airport menu now shows the signal strength of all available wireless networks. Small change, but incredibly useful.
• Docksposé is pretty cool, but I think Windown 7's "Peek" is better!
• Much, much better sleep/wake performance on portables (I worked on this issue more than anything else).
• QuickTime X. I think it's safe to say that the "Marble" interface in 10.7 will be black, and look like QT X!
• Native support for 4-finger gestures, plus an API for application developers to build multitouch directly into their apps! (This makes my previous post unnecessary, no more hacking is required to get 4-finger gestures!)

Of course there are some issues with 3rd party compatibility. During testing it was incredibly frustrating that I would know that a certain application wasn't working correctly in SL, yet, due to the Non Disclosure Agreement, I wasn't permitted to email the app's author to let them know. Hopefully, for the better-maintained apps, we'll see new versions that address SL compatibility in the near future (Growl 1.1.6 for example, and Adobe CS3 too!).
Overall, it was a very rewarding (and often frustrating) experience to take part in SL's testing and development. It's satisfying to think that bugs I discovered have been corrected, and won't be present in the consumer build. It's incredible how responsive the developers were to bug reports - it really encouraged me to WANT to test the OS more. I hope I'm able to get into the 10.7 testing program!