+1 tageater
Done it both ways, had it done both ways.
Old friends have histories that kind of flatten the "you owe me" accounts differently than acquaintance and new friends. I'll always offer and I appreciate it when they offer some kind of compensation or equalization method, regardless of the kind of friend, new or old. The offer is generally more important to me than actually receiving some kind of renumeration. It's just good to know they recognize your effort and your contribution.
Bottomline, IMO, if your doing it because you love it and want to be involved, don't keep score. If your doing it for some other reason, let it be known up front, everybody goes home happy.
DC