Browsing in Finder is extremely slow while fine in Terminal I did Repair Disk Permissions, reindexing files for Spotlight, and remove cache folders but it's still broken. It takes 30 seconds to several minutes to files to show up in local, not remote, folders.

Also tried to boot in Safe Mode but it was the same there.

I've used this MacBook Air for 10 months and it wasn't a problem for the first 9.5 months. I can't figure out since when it's been broken and what's caused the problem.

I'm using MacBook Air (mid 2011) and OS X 10.8.2.

Do I need to reinstall the OS? I have Time Machine backups and I've heard that you can restore from Time Machine backups after reinstalling the OS, but what if that also restores the problem back?
I found it. It was automounted NFS shares that makes Finder unstable (even for local folders). I used hard,intr mount options so the disconnect dialog was not showing up. Now I use crankd in PyMacAdmin so that they are only mounted when I'm in my home network.