The group seems to travel faster by moonlight.
- New Moon: no bonus.
- Half-Moon: take the average of all the party members' speed, and add +5 feet to that. (Yes the dwarf does still slow you down, but not as much.)
- Full Moon: As long as they stay together, everybody in the party uses the fastest member's speed.
Always: no penalty to Perception &c checks due to lightless or low-light conditions.
The group can see perfectly fine by moonlight, but their enemies cannot see them: enemies are treated as having Human senses when trying to see the Party in moonlit conditions.
Everything above assumes the Party is in a place where moonlight can reach; won't work in caves or window-less rooms of buildings or in dungeons.