It has been 2 months since I started working with the latest Kubuntu, and I can now draw some conclusions.
1. Kubuntu itself, compared to Mint 7, looks less polished — in terms of fonts and drivers. 2. ATI drivers are a whole other story. I forget where I read it, but it turns out that ATI, starting from a certain kernel release, dropped support for my graphics card. So I have to use the open-source drivers. (And curse ATI.) 3. Things crash from time to time. Mostly Kvpnc and Krdc — the VPN frontend and the RDP/VNC tool. Annoying, though I take comfort in the fact that nothing like this ever happened in GNOME. Nothing else seems to have crashed. 4. The KDE 4 taskbar couldn’t be configured for vertical placement — the icons scale in a strange way. 5. X.Org starts growing and eating memory. It’s unclear whether it’s due to uptime or some software corrupting it. I don’t remember this happening in Mint, but on FreeBSD the laptop could run for weeks without any issues.
I’m almost ready to go back to the old Mint 7, but this time — to its KDE edition. I’ll install it in a VM and see what version KDE updates to there.