Quoted from the above site:
While in general, alright can be found in all the senses of all right, in
practice there can be a real semantic distinction between the two, because the
two word form all right can mean 'all correct' or something like that, while
alright can only mean 'good; safe; healthy', etc. when used as an adjective.
(Similar distinctions are found with already and all ready, though these forms
have diverged to the point where they are not interchangable at all.) Thus the
sentence "The Kids Aren't All Right" can mean 'not all the kids are right', or
'some of the kids are wrong', while "The Kids Aren't Alright" can only mean 'the
kids are not OK'. from http://www.randomhouse.com/wotd/index.pperl?date=19990604