So far, the biggest drawback is the not being able to utilize its primary appeal (social network) - there are not many people that have GoogleWave. Since you can't get it without an invite, not many people are on it. If you would like to join the test group (by getting an invite), just include your email in the comments sections (once you join, I'll delete your 'published' email). Also, you NEED to have an existing google account, as well (gmail).
The real-time 'threads' (think of a message board of something) allows any type of attachment and you can revisit subjects at will, splinter off discussions into new threads, invite others into the discussion, etc. We're currently having issues with the video attachments, but everything else seems to work fine (make sure you download and enable 'google gears' for active content).
On second thought, forget it.
After a rather pleasant run-through on Friday, today I experience a bug that freezes the browser it operates in (due to uploading navigation). It appears this is a known issue with the Google folks as they reference a slew of Chrome incompatibilities and bugs that plague this application.
Opening the wave applet in Firefox fixed the scripting error experienced in IE7. Still having issues accessing video between users.