I think Apple going to release Mac OS X Lion on the 1st of July and I can’t wait! My Mac is pretty messy and I haven’t performance any clean install on my Macbook since day 1 I got my Mac in April 2009.

Upgrading to Leopard
I did not clean install, in fact I just run the disk and let Apple to magic. System was stable and so I continue using my system.

Replacing HDD
When I change my HDD I wanted to do clean install but I use Carbon Copy Cloner to duplicate a whole working system instead.

So after 2 years, I think its time I do a clean install.