Does constant charging harm my Macbook Pro?

Solution 1:

See http://www.apple.com/batteries/notebooks.html. This link suggests that you should fully discharge and recharge the battery at least once a month. I did not see this on that page, but I read somewhere that it is ok to leave a mac plugged in for an extended time, so just make sure you exercise the battery and let it completely discharge every once in a while.

Solution 2:

Anecdotal evidence (i.e. my own experience) suggests that it's not very harmful. I have a white MacBook 13" from 2007 and my battery still manages a good 5 hours (it did around 6.5 when new). I leave it on the charger most of the time, but about once a month (sometimes twice, sometimes once in two months) when I take it with me, I just let it sleep when I deplete the battery. That way, it will completely drain. After that I always make sure to fully charge it.