In reply to remtherockclimber:
Sometimes - on other crags, if its hot, if i'm climbing really easy stuff
Yes - always on multi-pitch or crags where there is a lot of loose stuff.
On a bold route towards the end of last summer I wished half way up that I was wearing a helmet and I've found since then that when i am climbing challenging/bold routes that a helmet is quite comforting and I worry less about the consequences of falling.
Have worn one more this summer as I've had a mate's spare one after it got left in my bag last time we climbed and i'll be purchasing a shiny new one of my own this month.