This may already be common knowledge, but I noticed last week that an iTunes purchase (erm, made by myself... had an old Def Leppard tunes craving) did not track for a few days. The click tracked, but the sale took about 5 days.

It finally showed up at about a day after I received my bill from iTunes. So I assume that iTunes doesn't report the sale to Linkshare until they process their billing.

FYI if it helps anyone :-)