Hardware compatibility, as others have said, has to do with the kernel and what drivers were compiled with it. I don't know what Ubuntu comes with, but that is where you look for hardware compatibility problems. Linux itself supports more hardware than windows does. I have hardware working under linux that does not work under Windows because there are no drivers for current versions of Windows. You might want to go to the Ubuntu forums for more specific help with your issues.
Performance is an entirely different beast. Is the desktop slow? Is hard drive access slow? What kind of performance problems are you having? There are many different types of performance problems, and they all have different solutions.
Most Linux distributions default to KDE, which is unfortunately becoming slow and bloated. They added a lot of eye candy and found, just like Microsoft did, that this can put performance in the toilet. You can turn off a lot of the eye candy, or you can switch to xfce or gnome, which are much more robust.
I personally use Slackware with xfce. Slackware comes with a kernel called the huge kernel because it has every driver under the sun compiled into it. This does not impact performance, but everything works without me having to go find drivers. Xfce does not have a lot of eye candy, and it is very fast and responsive.