what if somebody will accidentally delete .svn folder in main svn checkout directory? :roll:...
That''s a good question to which i do not have an answer .. and this would _never_ happen to me anyway

Nah, seriously, i had the same problem and i don't know another answer to that but to checkout the whole thing again

...
... but maybe one can save the whole directory, and try checking out only the top files lijke this:
$ svn co http://....../ufoai_2 # <-----break it after the first few files, so the .svn dir is back.
# copy the saved directory over ufoai_2
$ svn cleanup
$ svn up
But i don't
know if this works at all.
EDIT: Also
maybe a
svnadmin recover
could help here.
Werner