Nope. I'm hard-wired gigabit on the 27" iMac (early 2010) and the 15" Macbook Pro (late 2013) has been fine.
They sure flattened the UI though. I like the changes made to the guts of the OS (better prioritization and combining of background task calls, etc.) in that they make the same machine seem quicker. The UI is a mixed bag.
Not unlike the move from the colored Apple logo to the sleek silver one. But the 10.9 UI wasn't as gaudy as the rainbow Apple so I'm unsure the motivations behind the change other than simply to make 10.10 stand out as "a big change".
It's not a deal breaker though IMO and the improvements are worth it (again IMO).
I did have to turn on speaker feedback when using the volume controls. Seems the default is now to just change the volume with a visual feedback only. To me that's not enough info to know how loud/soft the volume is. It's an easy fix in Settings/Sounds.
---update---
Right after posting this, I got an e-mail from a friend. The 10.10 upgrade broke his Adobe Illustrator (unknown version) so he's going back to Mavericks. I have Photoshop but not Illustrator so wasn't aware of that issue.
Outside of that I've not run into anything that didn't work or that wasn't quickly fixed (Wallpaper Wizard)... with one conditional exception.
Using Trim Enabler so trim works with 3rd party SSDs means disabling KEXT (a security feature - globally) so there's that concern if you use Trim Enabler.
http://www.cindori.org/trim-enabler-and-yosemite/