My half marathon history is as follows:
2003 - trained hard, torrential rain, Time 1'50"49
2004 - didn't train as hard, beautiful weather. Time 1'50"01
2005 - intended to run again, got shin splints and sore knees.
2006 - got fat :o(
2007 - was finishing up Masters and not exercising
2008 - late entry, attempted to kick start myself into exercise. Gorgeous day. Time 1'59"10
I was very happy with the run given I hadn't really trained properly, and best of all I really enjoyed myself. I'm seriously considering the full marathon in September. First though, a week off to let my sore legs recover :o)