My experience has been with the inverse of this, though. I've been seeing Microsoft and friends reserving literally thousands of patents on things that aren't even tangentially related to anything they're working on, in language so broad it rules out huge areas of development.
This is true, however for these large companies many of the patents are filed as a defensive measure. Its fairly uncommon to hear them sue someone for patent infringement, and they probably have a patent on just about anything (MS has a patent on the strlen algorithm for example, its really insane).
In other words, worry about getting sued by a patent troll not a big company. Also, perversely, I think you better off not even looking for patents in the first place because one of the factors that can go against you in a patent lawsuit is whether or not you were aware of the patent in the first place.
