Slashdot has a great little write up named Google and Yahoo Creating Brain Drain? The /. links to a Business Week article where it says "In the second quarter alone, Google snapped up about 230 engineers."
In a Cre8asite Forum thread EGOL gives the perspective from a professor, which is pretty enlightening...
Every semester you have couple hundred students in your courses and most of them are average - the typical student. A small number are very bright... and maybe one or two will be absolutely off the scale in their intelligence, work ethic and driving vision.... a few of those will be inclined towards very practical problems... then a tiny fraction of those will be highly interested in information technologies. In an entire teaching career you might see a couple who might fit what it takes to work and perform well at one of these companies.
The very smart companies come to campus and ask faculty: Who are these students? These companies pay well - perhaps double what the typical company would pay - and these highly motivated students will happily go work for them. These companies are very astute because they get 5x the productivity for just 2x the cost. But more important is that they get 100x the vision and innovation at the same time.