Can I leave it plugged in for charge all the time? -Samsung Galaxy 3 I5801
I don't know about your specific device/battery but here is a rather detailed article on the battery in android phones and the app used in the article to log battery information is called CurrentWidget

If the article is representative of most smart phones, which I suspect it is, to maximize your battery life your phone does an initial charge to 100% and then maintains the battery at about 93%.

My takeaway is that it is good to leave your phone plugged in and charging when you can but it is not good to frequently plug and unplug your phone.