Whenever a larger company (e.g. Google, Y!, Microsoft, Facebook, or the like) is trying to buy a smaller company (e.g. Twitter, Facebook 2 years ago, Myspace, etc.) a leading indicator of interest is the fact that the company execs all suddenly sign up for accounts on the social media service they are trying to buy.
E.g. when rumors abounded about multiple companies trying to buy Twitter, I suddenly saw a bunch of execs from a not-to-be-named-here company join Twitter.
Indeed, I am tempted to create a list of email address of top execs at different companies I know, and run this through the email scrapers of various services periodically to see where M&A interest (or cloning of functionality) is about to occur.
If anyone wants to automate this and share results, let me know, could be an interesting view into what is the next hot (or soon to be acquired) company in the valley is.... :)