Primarily for talent (the big guys are dying for innovation and they are paying for it) and client lists (prove your end user customers actually like using your software versus just being a business need). Sometimes it indicates the potential of an "untapped" market and I would see these acquisitions as getting a horse in the race (when Gamification/Social Enterprise blew up for a bit and you saw everyone buy a horse).

Prove people love using your software and you can get acquired if you want.