Live is definately worth it. I have found my "solo gaming" makes up about 25% of my gaming time now. 75% is dedicated to Live.
Human Opponents beat AI every day of the week, plus you get to play with your buddies like they are sitting beside you.
My best advice for live is cultivate a great Friends list and stick with it. Otherwise you may run into a 12 y/o kid with a mouth like a sailor.
