Aside from the price there are three factors that come into play:
1.) The Treo 700P runs Palm OS while the Motorola Q runs Windows Mobile. (The Treo 700w runs Windows Mobile.)
2.) The Motorola Q has over half and hour more talk time and between two and three times the standby time.
3.) The Motorola Q lacks a touch screen, unlike the Treo.

If you want to take hand-written notes and run programs that require a touch screen then the Treo is your horse. Otherwise I'd go for the Q and save the money.

Hope this helps,