When I try to lunch my MacBook Pro I can see a progress bar on loading screen. It goes to 1/15 or something like this and then it shut downs - I cannot reach even login screen. It happened to me 2 months ago, I have 'fixed' this by formatting my hard drive and installing OSX (Lion) again.
This time I think that situation is a little bit different - I am able to enter single-user mode by pressing cmd + s. I then type /sbin/fsck -yf, I get the error:

** Checking Journaled HFS Plus volume.
   The volume name is Macintosh HD
** Checking extents overflow file.
** Checking catalog file.
   Invalid node structure
(4, 24704)
** The volume Macintosh HD could not be verified completely.
/dev/rdisk0s2 (hfs) EXITED WITH SIGNAL 8

but when I type exit, I can the login screen and I can log in. I tried a lot of things, booting from recovery partition and choosing disk utility to repair the disc, but I get error that it cannot be repaired. I have googled for hours and the only real solution I have found was to buy Disc warrior that might fix the issue. Any other suggestions?

Secondary question is what causes this issue? I thought the reason are bad sectors, but Smart Utility haven't found any. I found suggestion that RAM could cause this kind of issue as well, so I downloaded rember and made memory test - all tests passed. Right now I have used my solution of entering single-mode user and then typing exit, however I am not sure how long it will 'work'. Of course I have back-uped what I considered important.

Thanks for the help in advance!

UPDATE: I guess Smart Utility was not very useful, I mnaged to get input/output error, which I believe is equivalent to bad sector.