The UI could more usefully inform users about mis-set clocks
After changing my pc time manually one hour ahead to comply with the DST change in my country, Tor could not find any .onion sites (WWW still works)
All the information I could get was a warning from the message log: May 12 21:26:37.484 [Warning] Received directory with skewed time (server '188.8.131.52:9090'): It seems that our clock is ahead by 1 hours, 1 minutes, or that theirs is behind. Tor requires an accurate clock to work: please check your time, timezone, and date settings. Which in fact drove me to the solution, by reverting the time.
However, this is not clear enough to the average user, so either there is a bug with handling manual time, or the user needs to be made aware that he must set the clock automatically.