In reply to Rob Exile Ward:
We aren't comparing Cardiff with Sheffield or Leeds though are we. The Wye has plenty of decent routes, Ogmore has enough adventure to last a lifetime, there's a whole mixed up variety of sport stuff in the valleys, even if the location isn't tops, plus a range of bouldering. And the amount of stuff within easy (sub 2 hours, say) day trip reach encompasses Avon, Gower, and lets face it Pembroke ffs.
London might edge it on wall quality, although I'm told the one in Cardiff isn't too bad, but there's nothing much for evenings unless you are on the right side of town for the sandstone (in which case you're the wrong side for everything else), and a reasonable drive is needed to get to Avon/Peak/Swanage for days out. London has the advantage of lots of psyched people for trips away, which can be harder to do of there's tons on the doorstep, but then that's because there's nothing on your doorstep.
For only climbing purposes, I'd move in a snap. Without having lived in Cardiff I can't really compare much else...