I leave GTalk running all the time. I've even added it to my ignore list on TasKiller, so as to keep my phone's memory at max. I use TasKiller to free up RAM AND kill unwanted tasks.
However, I also have to set my Notification Ringtone to Silent. After all., why would I want a zing, bing or tada when I connect my USB cable to my PC.
What's more important to me is going into my Handcent and GTalk apps and setting the ringtone and volume for each app. That way I know what type of notification I'm receiving.
I can tell when I receive a GTalk update or an SMS/MMS message.
In my opinion it makes sense to have different tones for SMS/MMS or GTalk, as well as different volumes. Therefore, I suggest you should have a different ringer volume from your notification volume.
To set these.
From Home Screen
Menu
Sounds & Display
Ringer Volume
[ ] Remove tick from Use Incoming call volume for
notifications.
Then from within each app set your own volume.