It not a question about services--it's a question about potentially chatty network connections. IM connections aren't high bandwidth, but they do frequently send keep-alives back and forth. (I'm assuming that the built-in GTalk client is built specifically with this in mind and operates on a push system like the GMail client, and so it has minimal impact on battery life.)
The only feature I really want is to be able to "name" my contacts within the buddy list. That is, if an entry in my contact list on the Droid has an AIM username attached to it and that username appears in the AIM client I'm using, it displays their real name so I'm not forced to remember 50+ AIM screen names.