I notice that the lower left hand corner of my of near my keyboard is very warm while my ibook is plugged into the AC adapter is that normal. There nothing blocking the vent
It gets hot there because thats where the hard drive is located and it gets hotter when it is connected to an outlet because by default, it is set to never go to sleep when connected and to go to sleep when possible when in battery mode. You can change this by going to System Preferences>Energy Saver.
Mine's pretty hot right now but to be fair, it's been up and running about all day converting music, typing essays and messing around on the net (this forum included ) albeit it is about 36 degrees celsius here.
As someone said before, the front left corner is where the hard drive is so it's kinda comforting to think that it's all working well and good - even if it is a little warm. If you're really worried, go to: http://www.versiontracker.com/dyn/moreinfo/macosx/19994
Download the program and tell us what sort of temperatures you're running.