This weekend I took some time to have a look at Ubuntu. I find Windows Vista is very slow and I wanted to know how Linux would run on my machine (Acer Aspire 5315, Intel Celeron 1.7 Ghz).
I downloaded a CDRom from Ubuntu's website. You can boot from that CDRom and run Linux without making any changes to your machine.
Directly, I was convinced by the performance : Linux is much more reactive. When applications are slow, the OS isn't and that makes all the difference.
There are however some things that make me realize it would cost me time if I would completely switch to Ubuntu :