I have been running Ubuntu 15.04 for about six weeks now and I must say it is GREAT!
I’ve only run into one issue and that was getting Spotify to work. Using this GNU/Linux distribution has really opened my eyes up to how bloated and inefficient MS Windows can be. I am running on a Dell Latitude D630 (old laptop at work). I have yet to experience the laptop freeze or leave me waiting to perform a task unlike when I had Windows 7 installed on the same hardware.
The most resource intensive program I currently use is Google Chrome not much different from when this laptop had Windows 7 as its sole operating system but, there is a huge difference in the overall performance of the hardware now.
Breath new life into that old PC that is sitting around wasting away, try out a GNU/Linux Distribution you may find it quite enjoyable.