SESSION variables: How much is too much?

Hi, I'm trying to learn php mostly by reading the docs and pulling through other peoples projects for reference examples. One particular application I'm looking at has a ton of variables being handled through the SESSION global variable, probably about 25 or so variables. That just seems like alot. Since I'm pretty new to php I was wondering if this was typical and acceptable or if there was another best practice for maintaining large amounts of information throughout a session, like maybe persisting a temporary object in the database and passing a connection...or something. Or is just passing around a pile of variables directly in the SESSION object better? Thanks, Mark