Using mod tools make this kind of list easier to make. Anyway, for February, here is the break-down of where questions were migrated away from ServerFault. I didn't go into any additional stats (mod-hammer vs. vote-to-5) or what happened when they got to the destination site since I'm on a crap network and that kind of loading may just kill it.
Destination | Count
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StackOverflow | 14
SuperUser | 133
Meta.SF | 1
WebMasters | 40
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Mod-moves to any site:
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AskUbuntu | 5
Apple | 3
WordPress | 2
Unix & Linux | 8
WebApps | 2
Security | 1
209 migrated questions, of which 63.6% went to SuperUser. What's interesting to see is that migrations to WebMasters outnumber migrations to StackOverflow.
Moderators do have the ability to move questions to other sites, and 10% of 'em have been. If a question is a generic Linux question (example) that has to do with the inner workings of Linux and doesn't directly touch on sysadminly or end-usery things, mod-flag as a migrate to Unix & Linux. As you can see, we get a fair number of those. SuperUser-style questions regarding Ubuntu may be a better fit for AskUbuntu, although that question hasn't been fully resolved to my knowledge.