Professor poaching is something that is quite widespread throughout academe. I see it all the time at Columbia (usually from the perspective of the poacher).
From the side of the poached, however, large public universities are being forced to create special funds in order to keep highly productive, high profile professors who are getting outside offers, and this in a down economy. And they seem to be doing a good job. According to an article in the Chronicle, many of the major public universities are retaining about 75% of the faculty whom they give a counteroffer. They don't give counteroffers to everyone (sometimes the offer from the other institution is just too good to match or beat, and they don't bother with institutions they perceive as less prestigious). But money is only part of the strategy. They are matching some of the poachers' benefits--things like reduction of course load, increased graduate students, increased teaching or research assistance, and simply making sure they receive higher merit pay increases (evidently, one problem in this economic downturn is that recently tenured, high profile associate professors are often making salaries close to recently hired faculty, making them want to look elsewhere). If that doesn't get you, then perhaps a coveted parking spot would!
See the full article here.