Today I had a problem with storing cookies in Safari 4, in every other browser (including Safari 3) the cookies would be saved, however in Safari 4 the cookie would not save. The cookie I was trying to save was a CSV list of values like:
,item1,item2
The list of values started with a comma and this turns out to be the problem. If you have this comma Safari 4 will create the cookie but will not save the data, so you end up with an empty cookie.