Through the power of 10K tools, I bring you statistics:

    Outbound Migrations last 7 days
            Total  Closed  Ignored
    SU      19     1       9
    SO      2      0       1
    Web     1      0       0
    Others  4      0       0   (Mod-initiated: Unix, ITSec(2), WebApps)
    Total   26     0       9

Closed = Question was closed on the target site<br>
Ignored = Question gathered no attention on the target site

As you can see, our biggest export are questions to SuperUser. Just under half of them get ignored when they get there. We've actually migrated as many questions to the beta SE site ITSecurity as we have to StackOverflow. If this keeps up, and Security.se gets out of beta, we just might have our 5th migration target.

    Inbound Migrations, last 7 days
            Total  Closed  Ignored
    SU      8      0       2
    SO      33     0       9
    Web     5      0       3
    Others  0      0       0
    Total   38     0       14

Unsurprisingly, StackOverflow is our biggest importer. Just over a quarter of those questions go ignored, and none (in the last 7 days at least) have been closed for some reason.

Both directions, questions usually have answers from the originating site that ship with the question as part of the migration. Sometimes these migrated-answers are Accepted on the target site. 

----
For having a slightly better overall answer percentage than we do (81% vs 80%), questions we send to SuperUser languish unloved almost as often as they get the attention they deserve. We're a lot better about answering incoming questions. 

What are the questions that tend to get ignored? *Badly asked questions*. While it may say "windows home server" somewhere in that mass of incoherence, that doesn't mean we have to send it to SU to die. The one actual close was a close-as-dupe that our own all-rounder [Dennis Williamson][1] helped euthanise. 

So please, when voting to close, if it is a crappy question just close it. Don't take the easy way out and send it somewhere else. 

  [1]: http://serverfault.com/users/1293/dennis-williamson