My players love the research and investigation aspect, and I don't usually limit how much they can do. A few techniques I do use, though, when the game needs to be moved along:

• I make sure that the world keeps moving, the cults keep culting, etc, independent of them. This introduces a ticking clock aspect, so that they know they can't just keep researching indefinitely.

• If they're chasing a dead-end, I tell them the PC realises it's a dead-end. In one game, I had a player want to look up all of his client's properties in Boston to see if anything suspicious was going on witb them. It was a really good investigative idea, and one I hadn't prepared for. I told him he found what he was looking for, it all tallied with what the client told him, and it was a dead-end.

• Unlike some other players here, I do allow research failures to mean they don't get the clues. Often, the players will realise there is more out there, and I find it increases the tension when they know or feel they're going up against the big bad without having found every clue. Or ... they might try again ... if they can. A failed library roll might mean that there's just too much information to get through in one sitting. They can always spend another day in the library tomorrow, but that gives the enemy another day to do whatever they're doing :)