In reply to Doug:
I upgraded the other day. It went pretty smoothly. Mavericks was such a good and stable system that it is hard to improve on I think so it is mostly just tweaks.
There is a problem with Java Runtime if you use any of the Adobe Suite. Apple don't like Java so it isn't installed and you need to install it to get rid of the warnings that it is missing each time you open an Adobe product. I ended up having to install two versions because of the various Adobe packages.
This discussion covers it -
https://discussions.apple.com/thread/6602999
The other problem I have experienced is that Safari went slow and started beachballing on me. Again, this one appears in discussions here -
https://discussions.apple.com/thread/6603972 and the solution offered there worked for me.
Can't comment on the wifi problems since I only have it on my desktop at the moment which is connected direct.
In general it seems ok in other ways but nothing sensational. The colours have all gone bit sickly on some of the Finder icons. Nothing has stopped working randomly like it used to with the old Cat-themed systems.
Alan