To see info about or manage any app:

1.) From the home screen, press the menu button on your phone. Then hit the Settings button on the screen.
2.) Choose "Applications" -> "Manage Applications"

"Downloaded" tab - The apps you've downloaded to the phone (everything except system apps or pre-installed apps)
"Running" tab - Apps that are running in the background on your phone (and possibly using up unnecessary RAM
"All" tab - Includes system and preinstalled apps. If you can't find it on "Downloaded", it's in here.
"On SD Card" - the apps you've moved to the micro SD card.

When you tap a specific app, you can see the version. You can also stop the application (for apps running in background), uninstall the app (or updates to pre-installed apps), clear local data (deletes settings, be careful of this), move to SD card (only for apps that support relocation), clear the cache, and clear launch defaults (meaning settings about which files open in which programs by default, linked to the "Open With" screen you'll sometimes see).

I'm not sure why people say the market app is 'wonky', but I guess they mean it is kinda awkward to navigate around or possibly has problems displaying apps. If you choose "uninstall updates", the app will go back to the way it was when you first got the phone. Be aware, though, if an app is set to automatically update then it will do so when you're connected to the internet.

Let me know if I missed anything or if that was too complicated.

 

I dunno about wonky, but it's definitely annoying. There's several Google apps that I do not use (Maps as an example, which takes up 10MB or more of space), and when I untick the box for auto update, the Market updates it anyway. I was constantly uninstalling the updates because the Market kept updating it.

I finally had to uninstall the Market update (freeing up an extra 7MB) and install AppBrain. Now, nothing updates unless I want it to.

Without hesitation I can honestly say that I hate the new Market app. AppBrain is much better for updates and you can also move it to the SD card.