I have a guy playing a ranger, who really likes the flavor of using a crossbow instead of a longbow. However, as we all know, with RAW a ranger is basically crippling himself by choosing to use a light crossbow instead of a longbow: he has to spend a feat on Rapid Reload, just to get on equal footing with somebody using a longbow.
I think that having to burn a feat just for flavor is not a good thing. So here's what we do in my PFRPG game:
TWEAK: If a crossbow is used by any character who is proficient with martial weapons, that character gets a +1 to hit with the crossbow.
This way, light crossbow + Rapid Reload is roughly the same as longbow + Weapon Focus, and nobody is screwed for wanting to use a crossbow instead of a longbow.
And of course, characters who are inept with martial weapons still get to use the crossbow as a "point and shoot" ranged weapon, without the +1 bonus.
Anyway, thought I'd share that. So far, it's the only house rule we've come up with that seems worth telling people about. :-)