I also wouldn't worry about it, though I might be completely wrong! I leave mine plugged in the majority of the time, since I seem to use it throughout the day and evening (the joys of being unemployed). I'm more worried about charging cycles, as this is what eventually leads to battery replacement. That probably won't occur until at least 500 recharges, but the longer I put it off, the better. However, I suspect that after 500 recharges, I'll be ready for the next version of the Nexus 7!
The only disadvantage to leaving it plugged in while using it (besides lack of portability) is that when it's at 100% battery charge, using wired headphones results in significant, annoying static. If it's not at 100% yet, everything sounds fine. I don't think this is due to a defective unit, as my first two units (returned due to bad screen lift and a very blown speaker) also had the problem. I think it's just an overall Nexus 7 problem. I've been meaning to search the forums about this issue. I guess I need to get a Bluetooth headset.
Sent from my Nexus 7 using Android Central Forums