Practically - as little as possible. The general community consensus has been to educate and delete blatantly off topic posts.
Meta also sometimes gets used as a soapbox for ranting about moderation decisions. It's probably better since mod messages were made anonymous - but generally, if a post looks or feels like a direct attack on someone, it probably needs to go quickly. It's sometimes a bit iffy - as a mod I'm happy to explain decisions but sometimes folks need to make the call to whether you're getting through to the poster.
Nuking is deletion. Mechanically a spam deleted question is the same as a regularly deleted question - only you need to click through to see it in some cases.
More or less if you feel having the post visible does harm to the site, vote to delete. Otherwise just let nature take it'sits course.
