Installed on 5 Macs here without any major issues so far, all quite different
with very different purposes.
Have come across 1 minor issue (some would call it a "sky is falling issue")
is Adobe Bridge CS6 (and apparently CC) will not automatically upload from
cameras or recognize them. Yet Adobe Lightroom does (great reuse of code Adobe).
I was able to use Image Capture and even my ancient Canon upload tool (again kudos to
Adobe for making long term usable code for such a basic function). As I said I consider it
minor as there are very quick and easy workarounds for it until Adobe deals with it (if they ever do).
If you decide to upgrade, at a bare minimum, back up all of your data (should be doing this anyway). The majority of upgrades
go without issues however any thing can happen. In addition, make sure any apps that you depend on are
compatible with El Capitan.