• Having the client open for more than a few hours will use many gigabytes of memory (I'm at 2.5GB right now)

  $ ps auxw |grep -i Message
  jordan   73227   0.0  1.4  4037928 113476   ??  S    13Apr13  13:21.86 Messages*

I've had Messages open for 17 days now and it is using 111 MB of memory (that's RSS, VSIZE is 3.85 GB). I have 4 accounts (three jabber + iMessage).

I don't know much about your other problems. My biggest problem with it is that it doesn't reconnect always when I start/end my VPN sessions, but other than that seems to work ok.

* Edited so it would display nicely.