Depends on the sort of party it is... anything too crazy tends to put me off, whereas if it's essentially just people having a drink and chatting at someone's house with a bit of music in the background, no worries.
Last one I went to (I left about 20 hours ago) was of the crazy variety, complete with incedibly loud music, lines of white powder, and my hopes of getting together with a girl I've been kind-of-seeing totally dashed. I actually left and had to hang around at Manchester train station for 6 hours.