If you are worried about cleaning the table of tempusers, that's not hard.
You can just use a CRON job or similar to go out and remove all tempusers that have had no activitity in, say, the last day (or hour or whatever you choose). That is, if a tempuser hasn't been converted to are reguser, that must mean that he/she didn't finalize the order.
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.