I have specific periods where i have tests. I also work in weekends, but when a date is set (even if it is in a weekend) i can probably arrange i have a day off.
Most easy for me is when i have vacation/holidays.
Anything in EU is fine. I think somewhere centralized would be nice, or somewhere that is relatively close to everybody. Ie, when 2 are from Germany, 1 from Netherlands and 1 from Southern-France then i think somewhere in the middle (Belgium perhaps) would do fine.
Anyway, thats just a speculation.
Something i would like to add to Asp's proposal, i think it should be a yearly event at least
