There's inevitable overlap between U&L and SF. Generally, on the U&L side, we only migrate a question if it's definitely off-topic or if the asker agrees.

U&L generally isn't very strong on dedicated-server applications. For example only .6% of U&L's questions are about [apache](http://unix.stackexchange.com/questions/tagged/apache), contrasted with SF's >8%. U&L doesn't cater much for systems that people administrate through front-ends such as CPanel, usually we assume that a command line is available. Another kind of questions that will fare better on SF is practical performance questions (like [this question](https://serverfault.com/questions/305595/maximizing-throughput-of-virtual-file-systems) which was migrated from U&L to SF).

A large class of questions that can be migrated to U&L is shell scripting questions. Some of these feel generic on SF, because the techniques involved aren't specific to system administration. The same goes for package management questions. As far as I remember, SF has a good track record for migrations to U&L, so if you keep doing more of the same, that's fine.

The main thing to keep in mind about U&L is that programming questions are off-topic. If someone posts a unix programming question on SF, migrate it to SO.