In reply to seth:
Everything Chris has said is pretty much correct. The guidebook you need is the Alan Hill / Ian Smith one, but it's difficult to find. Luckily there aren't too many routes in Sark so I can scan it for you. Off the top of my head there's the following areas:-
Harve Gosselin - some long (200ft+) lines up to VS there. I've never looked at them so don't know if they're still doable.
Adonis pool area - we looked at these in the late 90s - some will still be OK for sure, but I don't know if the path down to them is still passable.
Venus pool area - these all appear to be still doable. There's an impressive overhang.
Les Autelets - these are a couple of stacks just north of 'the window in the rock' and had new routes done on them in the past couple of years. There's still space for more new routes I believe.
Victor Hugo cave - definitely some doable stuff here, possibly best DWSed.
If you're well-experienced with sea cliffs then give it a go, although I'm not aware of any climbers residing in Sark so I don't know who would partner you. It's possible that you might be able to rustle up a party from Guernsey to go over and have epics with you. (check out Guernsey Mountaineering Club on FB or message me) One of the problems is that although the island is all cliffs the topouts are bad - straight from steep rock onto steep gorse/hawthorn/brambles. Only parts of Little Sark near the venus pool and silver mine or L'Eperquerie common topout onto grass.
Bouldering - there'll be some on the beaches - Greve De La Ville, Grand Greve, Dixcart, Derrible. Landings are likely to be pebbly.
What would definitely be worth you doing is getting hold of a copy of the 'Guide to the caves and bays of Sark' which tells you how to do the sea-level scrambles and cave explorations. That's what I'd do if I was going there. http://www.sark.co.uk/the-la-trobe-guide-is-back-7636/
Be aware that if you do get yourself into trouble it's highly likely that it will end very badly unless you're the worlds best swimmer, and even then you're pushing your luck. Happy to give you any more info you require as best I can