Hiya.
With regards to the whole "player expects X, DM says Y...now player is screwed/upset" thing.
If a player has a character that relies primarily on some particular "schtick", the moment his butt hits the seat he should ask the DM how certain rules are applied. For the 'thunder cleric' example mentioned above, the *player* needs to ask the DM how he interprets X, Y and Z. For the thief trying to do the shadow-attack-backtoshadow thing...definitely ask the DM. If you are playing with a new DM, s/he doesn't know what your characters method operandi is...so it's your job to inform them so you all know what to expect. If it turns out to mess with your perfectly chosen skills/stats/feats/whatever, then you have time to adjust your play style...or at least you know what to expect.