I ask for these pretty much all the time. Not just to give the PCs hints, although that is a great way to feed information to them and I think investigative-themed adventures and side-quests should be utilized more in just about every campaign. But also because this is a great way to share part of the setting with the players that maybe they wouldn't be aware of outside of this context. The other side of this coin is that calling for Knowledge checks all the time can let you be a little sneaky and throw red herrings at the players. Maybe not 100% of the intel you're feeding them is relevant to anything at all. We had a "who's the werewolf in town?" adventure a few years ago in an all-dwarf campaign I was running and we had a lot of fun with them running all over town looking for evidence and accusing people. Their suspect list grew and grew, I think in part because they assumed everything I was divulging was a clue (it was not). They didn't find him.
How liberal are you with clues or hints? If an adventure or encounter is predicated on solving a riddle or some other kind of mystery, do you have a sliding scale for the XP reward, ticking off points for each freebie you have to throw their way?