I installed windows 8 Pro sometime last year, around November I think and so far so good. I love the start menu, so much nicer though I am of the opinion that it appeals mostly to those people with touch devices. That said, my machine is an HP Probook 4535s (not a spectacular machine of course!) but it is operating smoothly and the Windows Experience Index rating has significantly increased ever since I installed windows 8.
The apps are a plus especially the inbuilt music, mail, videos and photos apps! you can also download new apps from the microsoft store. Win8 also has faster startup it's actually noticable! SkyDrive integration is also another plus and its the new "in-thing" saving your documents on the cloud. Best of all, you dont need to worry about an antivirus, its got one inbuilt into its core and its actually good, its updates are very small
One main problem though is the way win8 has gone the extra mile to hide small but daily used things like the shut down button... Up until now, the folks at home don't know where it is and I usually have to shut down the machine myself...
All my external devices (printer, scanner, tablet, phone etc) are still working as before, I did an upgrade so no programs were removed and they continued operating as before.
Is it worth the upgrade? Well, it depends if you just wanna keep up with the times then go ahead it will offer a refreshed interface and notable speed improvement especially file transfer using usd, or discs. However, windows 7 is OK if you are not concerned about trends... functionality is basically the same (except maybe for the start menu!).
Hey don't just take it from me, here is a post from techradar that you can read to get more info http://www.techradar.com/news/software/operating-systems/windows-8-vs-windows-7-8-ways-its-different-1025285