Recently I've started leaving mozilla thunderbird running in the background while using my computer. I've been noticing thunderbird has been slowing down quite a bit and I recently realized its sucking up over 40 megs of memory! Does that sound normal for such a small simple program?

If it has a memory leak, this is possible. Try using something like PopTray to alert you to your incoming email and use Thunderbird to retrieve it rather than leaving it running in the background. Just a suggestion.

Yeah, I could just use the gmail notifier