I'm working on a project that will have a similar DB to how myspace manages friends.
I'm trying to determine the best way to build this out, as one user could potentially have hundreds of thousands of friends...
Would it be best to create an ID table that simply holds the UserID and the UserID of the friend? OR would it be best to just use longtext and hold all friends UserIDs in an array for a paticular user?
It is the correct way and most flexible way. With a longtext you have a VERY finite amount of references to users. Depending on how they are stored, the number available would literally vary because some identifiers are longer than others.. user 123 vs user 123456 for example.