What Laura said.

The only 'restriction' is on the Web browsing. . .the Kindle store access, book syncing, annotation backup, etc. are basic 'kindle functions' and should work with the Touch just like any other Kindle. The difference is that, on the Keyboard model, you can navigate to any web page . . .so, yes, you could
conceivably post on amazon's forums or even here. But it would be a real chore to do so. . .the browser is slow and lacks a lot of features most people feel are 'basic'. On the Touch, if you try to do that, no, you can't.
I'd also note that Laura mentions email. Lest there be confusion: You can't use a web mail client to check email on a Kindle Touch (while connected via 3G). You can on a Kindle Keyboard, though, again, it's probably not something you want to rely on for routine use! But both Kindle's have their own "send to" email address that you can use to deliver content to the Kindle. If it goes via 3G, there's a small charge, if you send it to be delivered via wifi (use the @free.kindle.com address) there is not.