rael: comments, meant to be constructive ok? and i've avoided php for ages now so really only general stuff
it's hashing not encryption; also, dont multi-hash things - it does nothing except chew resources - you want a salted hash
you're checking for magic quotes twice which is just a waste of resources - lose the elseif and just else it
surely a method that checks for the validity of something should return a boolean rather than a string? (check_email).
your naming sucks i.e. check_email - perhaps is_valid_format_email instead? slightly more verbose but it reads better, follows php conventions and allows for a consistent scheme e.g. is_valid_format_address etc.
naming your args the same as your methods is useless
meh.