Yosemite solved them almost completely.
Almost, because sometimes my 2012 MacMini will randomly disconnect from the WiFi access point (an almost 10 year old Linksys 54MBit AP-only).
Then, I have to disabled WiFi completely, wait a few moments, re-enable it and reconnect to my AP again.
It's very random, which leads me to the conclusion that it could also be an issue with the AP and/or all the wireless networks around me, probably using much later and much "better" technology and basically killing my WiFi.
I don't really blame Apple. There are so many devices out there, so many buggy firmware- and driver-versions, so many buggy OSs and the spectrum is so overloaded these days as everybody and his dog has at least one WiFi AP (sometimes several, via a mesh-setup or a simple repeater (adding to the problem inadvertently...). I sometimes wonder why works at all.