(I am putting this here so that the users experiencing similar problem can Google the solution)
My Linux PC (XUbuntu) started exhibiting a weird problem suddenly. After several days of uptime, most apps suddently started to take around 30 seconds to start up and they started locking up for 30 seconds when they accessed my local filesystem after longer time. Everything fixed itself after restart but I don't want to restart my main PC often.
I Googled extensively and found similar problems which were usually caused by networked filesystem or failing hard disk.
But this was not my case and I finally found the solution. If this starts happening, just issue the following command:
And it will immediately be fixed.
The problem is with gvfsd-trash app (which handles some kind of special access to your Trash Bin and you probably don't ever use it). You can find extensive discussion about this problem here on the Stack Exchange.