[emsy]

OS X is even worse. Up until Mountain Lion I could easily left my Mac on for weeks without needing to reboot (except for crucial updates). Since Mavericks and even more so Yosemite it has gotten out of hand. I need to reboot at least once a week, WiFi is broken and Finder regularly hangs up on me.

[joshuapants]

I'm playing with the El Capitan beta right now on a ~4 year old MBP and I will say that it seems very snappy and I haven't needed to reboot except for updates, and I haven't had any wifi issues (had a lot on Mavericks). That said, it's a clean install and I've been pretty gentle with it. I'm cautiously optimistic that they're improving these matters.

[zer00eyz]

At the os level I have only had a more stable system with every OS upgrade.

Wifi is back to its old happy self with the last few patches and seems more stable, Yosemite early days it was a bear I will give you that.

What I have found is that some things just don't play nice with the OS. Openvpn is kind of a bear and I'm not sure what the underlying cause is, but its easy to kill and restart so not a major issue there.

I do regular heath checks and cleanup though. EtreCheck is a great way to get a look at all the cruft in your system and make some calls on what to clean out/up!