if your going to America get it changed, you don't need to for the driving but you are expected to carry photo ID on you at all times in America and it's easier to carry a photo card driving license then your passport, especially if you lose it!
Your licence is perfectly legal to drive on in the US.
However SOME car rental companies may be iffy about recognising it. I've never had any problems (they just ask to see your passport as proof of ID) but have seen the odd report to the contrary.
Thanks guys - have just been to Direct.gov website and applied for photocard licence. Just hope it arrives before I go because I have had to cut up my old licence and send it in to DVLA !!