I've often set the Fix Version before the issue was assigned or fixed, because that's the way you can take a look at the road map in JIRA.
Which version do you set, then? The next version? In that case, I agree with the other comments that this can give a misleading impression that issues will be fixed even if they're completely orphaned.
We can try to make it easier to use JIRA to get a view of what is likely to be done by assigning a (tentative) fix version when an issue is assigned to a person and goes In Progress, as Gaul suggested.
Would that help? ap
