Yeah, I got some clue into the problem but don't know how to solve.
Actually Today I installed virtualbox on another kubuntu 12.10 machine. Right after that this machine also started taking long to boot and shows that "mount: / is busy" message. It also reminds me that the previous machine was working fine and shutting down gracefully till I installed virtualbox.
Please somebody suggest me what to do.
still looking for a better *nix?