The following PC rolls will always be made by me to keep things moving:
3. Sense motive
4. Saving throws
5. Group diplomacy
Player dice rolls of these types will be ignored, unless specifically requested by me.
I may make the following where appropriate, but you may request to make these yourself (let me know if you prefer to roll these yourself):
1. Knowledge checks
2. Survival checks
3. Individual diplomacy
Further, I may make a roll of any kind on your behalf if you do not post within the 24 hour timeframe (see above fore more on this).
Finally, a convention I have adopted (mostly for rolling during combat) in PbP games that I run is as follows:
1. No rolls during combat for any checks that do not specifically require an action unless called for by the GM. Same for free actions that do not influence combat. Eg. Knowledge (dungeoneering) to identify that ooze is a free action, but this is a roll you must ask the GM to make for you (unless he has asked for it). Concentration check to cast a spell is a free action, but that's fine to roll yourself (since it forms part of your cast spell action).
2. Always roll for actions in the order in which they occur. When in doubt, roll reactions to GM first, reactions to players next and then your actions. This should help minimize players swapping over save throws for attack rolls (and the like).
3. If you do want to make an "actionless" skill check, ask the GM to roll it for you. He'll have to post to tell you the results anyway.