Are you referring to battery life degradation from leaving your laptop plugged in? That depends a lot on the type of battery your laptop uses. The more recent Li-ion batteries are less effected by charge/discharge issues, but there can still be issues from heat, etc. If you are leaving your laptop plugged in and you are concerned about degradation of your battery, you can always remove the battery and run off of AC only.
I leave my laptop plugged in (with the battery), and I haven't noticed any problem. But then again, I'm not keeping a close eye on it either.
