All sites are reviewed.  Most sites are accepted, only about 1% or less are rejected for not following the rules.

No Adult Sites
No sites with nudity (unless medical or educational)
No sites that sell drugs (unless they are prescription that are discounted for poor people)
No Illegal Gambling Sites
No Hate Sites
No Illegal Sites, or sites that promote illegal activity
No Sites that are just a few words and a bunch of ads

Sites are usually approved within 1 week.  If you purposely put your link in the wrong category, it will be deleted, sites in the wrong category by mistake will be moved to the correct category.