Mark CMG said:
Do the characters in your game (whether you're a player or DM) spend much time between adventures and, if so, what do they do during that time? (Training? Carousing? etc.ing?)
When I DM, it usually depends on the adventures. I prefer long adventures that may took months for the characters to complete (like LotR), an probably span over a few levels. But necessity makes me run shorter adventures, usually with 1 level-up and taking a few days for the PC to complete.
Between those adventures I usually give enough time for the PCs to do whatever they want, such as crafting items for example. The downtime also helps explaining why characters have developed new abilities after levelling up, without the need to "roleplay training".
Mark CMG said:
Would you prefer it to be more time between or less or about the same?
As a matter of taste, it'd be better for me to have at least weeks or months between adventures. Otherwise, I would have to explain why the game stops at level 20, if it takes a year only for the PC to get there.
Mark CMG said:
Is experience available between adventures and, if so, what warrants an experience reward?
Well, if I need the PCs to be higher level for the next adventure, I have them level up during the downtime. I like thinking that the xp system is an abstraction, and people don't need to kill goblins before learning a new spell or crafting a magic item. The point is, it doesn't matter to me to explain how did they level up, they just got better somehow

After all, NPCs can be high level without the need to be all ex-adventurers.