We did our trip from Aug.18th - Sept.4th 2011. Climate was perfect, not too warm (mostly
) nor yet not too cold in mountains. Higher passes may be closed until June.
Yes, we heard same stories before our trip, that EU citizens are not allowed to cross border at Verkhni Lars (only border crossing between Georgia and Russia today), but finally we didn't have any problems. Do you need visa to enter Georgia? Georgia don't require visa from Estonian citizens, it may make a difference too.