It's a tough question, isn't it?  Is Microsoft buying Yahoo because of its long-term and broadscale expertise with open source?  If so, to what end?  Well, I thought, maybe what they're really buying is the expertise of the Yahoo programming team, akin to what I felt was happening with Sun and MySQL, et al.  Unfortunately, the theory doesn't seem to work here.

Microsoft's current stance on open source is, from what I can tell, to provide a compelling case to run open source packages on Windows -- that is, as long as we're leaving the Linux patent issue entirely out of the picture.  How they feel about open source on something the size and scope of Yahoo isn't clear at all -- and maybe that's why they want some existing experts in that field.

Perhaps what they're looking for are teams from Yahoo's side that they can put to work creating online applications -- to gussy up Windows Live, maybe, which as Paul McDougall pointed out, is horribly confused and confusing.  The incoherence of Windows Live is about as bad as the incoherence that swarmed around .Net when Microsoft unleashed that way back when.  So, perhaps the thinking goes, why not bring in people who seem to be natural experts at this sort of thing?

The problem, again, is one of clashing corporate cultures: Microsoft and Yahoo do not look, act, or think remotely alike.  This is a far deeper problem than I think Microsoft is willing to admit, retention incentives aside.  if Microsoft is doing this to get their hands on experts, there's nothing that says the very people they want most are not going to jump ship and head somewhere friendlier.

Perhaps Microsoft will jettison its existing online unit wholesale and simply swap Yahoo in for that -- well, maybe not all at once, but over enough time to allow some kind of transition from Microsoft's services to Yahoo's.  And again, therein would lie a huge and painful transition that would probably create as many problems as it solves.

Maybe the best way to approach this is just to leave the question open: What is Microsoft really buying?  The more I think about it, the more I'm wondering if even Microsoft knows by now.