Ha ha, funny you should post this - I'm doing a photobooth in a few hours, printing 4x6s with my big ol' Pixma Pro 9000 MKII. I've done it a few times in the past and I wouldn't recommend it 
Your big considerations are:
- Speed of printing
- Cost per print
- Reliability/backup
Some people say you have to have a dye-sub for printing speed. But the hardware is expensive and the cost per print is high, and having an identical backup just doubles your cost.
Some people use two identical cheap-but-decent inkjets and spool between the two. Keep a third identical one under the table in case one of the two breaks. Probably still cheaper for three little inkjets than one dye-sub, and cost-per-print is very small if you use the continuous ink systems.
For my needs, the Pixma 9000 is adequate. Heavy and clunky, not really fast, cost per print is low enough to be manageable (especially using LD inks instead of Canon). It's not unusual that I have to tell people "come back in 5 minutes for your prints." If photobooth business picks up enough to justify it, I'll find a better solution, but for only doing it a couple times per year it works for me.