I've often had a similar problem. I tend to run my games fairly fast-paced, in terms of the speed of the overall plot. It's just the sort of fantasy I'm familiar and enjoy, so my games often lean that way as well. In such instances, there's not much room for down time.
However, if I'm running a campaign of this sort, I let my players know in advance, so they can tailor their feats and characters accordingly.
Sometimes I do run slower, more "episodic" campaigns, and in those instances, I'm happy to work frequent down time into it. My problem then becomes that, since I give XP entirely by story awards and RP rather than by encounter, people who fall behind don't catch up unless I artificially inflate their XP. I'm toying with the idea of a magic item-creation system that doesn't cost XP, but just gives wizards a pool of "points" they can spend on magic items. Thus, they keep up with the group, and they can choose to create a constant stream of small items or save up for a few big ones.
Haven't gotten much of it down yet, though.