"Idiot troll me arse!"
No no no... not you Gervase...

"Is the whole claw actually removed?"
Yes... the common practice is front claws only...

"How does it affect the cat's ability to climb, and its general behaviour"
If you do it when they're kittens (The same time you spay 'em) they'll grow up never knowing the difference....   I've seen declawed cats that can climb like fkn squirrels... And as far as scratching behaviour goes, that has more to do with scent marking, and a declawed cat will still do it... only they won't wreck the sofa while they're at it....