Frankly, I'm surprised it took so long to happen. Or maybe I just didn't notice it happening much until now. When google pioneered contextual advertising, I assumed that the rest of the world would follow in spades. We'd be getting emailed, nudged, banner-added and text messaged whenever we displayed online intention or contextual curiosity. There is a world of nuance between blatantly unsolicited email spam and "relevant online communications," and I assumed that businesses would rush in to fill this gap. But I really haven't seen it that much. Until now.
Enter the Twitter Hawks. Businesses that hover on top of Twitter search terms and then @ you if you mention something relevant to their business. For example, I just got an @ message from an airport shuttle service when they saw me use the name of an airport in my tweet. Obviously, they're monitoring the public feed using Twitter Search or the Search API and replying publicly to tweets that mention airport travel in their business service range. But is this spam? Well, I suppose not the traditional type, but it's definitely unwelcome when my @ stream is filled with unsolicited business messages from orgs - no matter how "well intentioned" who are hovering over my communications.
Like any good enabling technology, people see opportunity and rush in to explore, address, solve, and experiment. I'm not surprised that people are exploring this gap, I'm just surprised it took so long.