I've got enough Grey Knights assembled to start playing games with the army and get a feel for what does and doesn't work. So far I'm enjoying it and plan to play it at WGC2011, but there's certainly room for fine-tuning. Here's the list I ran on Saturday's tournament at DL. It went pretty well for me still being new to a list with a lot of potential for finesse management (went 2-1 overall).
Grey Knights - 2000 points
255 - Grey Knight Grand Master - Blind, Rad, Psychotroke grenades, Psycannon
170 - Grey Knight Librarian - Might of Titan, Quicksilver, Sanctuary, The Shrouding
145 - Vindicare Assassin
159 - Techmarine - Orbital Strike Relay, 3x Servo Skulls, Rad grenades
250 - 10x Grey Knight Strike Squad - Psybolt ammo, 1x Deamonhammer, 7x Force Swords, 2x Psycannons
250 - 10x Grey Knight Strike Squad - Psybolt ammo, 1x Deamonhammer, 7x Force Swords, 2x Psycannons
250 - 10x Grey Knight Strike Squad - Psybolt ammo, 1x Deamonhammer, 7x Force Swords, 2x Psycannons
250 - 10x Grey Knight Strike Squad - Psybolt ammo, 1x Deamonhammer, 7x Force Swords, 2x Psycannons
135 - Dreadnought - Psybolt ammo, 2x TL-Autocannons
135 - Dreadnought - Psybolt ammo, 2x TL-Autocannons
The big things that felt like they weren't reliably contributing were the Orbital Strike Relay (which also made me want to not move the attached strike squad - something I didn't like) and the Grand Master. The OSR took out a land raider through smoke in game 1, but I felt like that was an extremely lucky and rare shot. The grenades on the GKGM were amazing, psychic communication was decent, grand strategy was only helpful one game out of three, and the GKGM's personal CC contribution was weak. The vindicare also underperformed all three games; in total, he destroyed one 85-point predator and the storm bolter on a 30-point drop pod. I forget if he ate a venom in game 2 before he died - I think the caltrops on turn 2 got him after the T1 shooting didn't, but I don't remember.
Here's a list I'm debating testing out. It trades the OSR, the GKGM's combat potential and Grand Strategy, and some GKSS upgrades for making one squad stubborn, more grenades, and a squad of purifiers. I feel this army will be more mobile and have stronger counter-assault despite losing the grand master. It does create one additional kill point, and is slightly less homogeneous than the previous list (IE: the purifiers can be singled out if they're in LoS, which I may try to prevent depending on how bad I need their psycannons). I dislike having to include another guy from the inquisitional forces rather than an actual grey knight (and not using my grand master model), but at least this guy is wearing actual power armor...
Splug 
