Carla Schroder (tuxchick) recently posted a Kubuntu critique on LinuxPlanet titled Krazy Kubuntu Annoyances. I saw this on both Linux Today and LXer.com but I'm replying here as commenting is annoying on both sites because they strip out most html tags.
I've been setting up an advanced home office network to replace my existing haphazard mess. I haven't been posing much lately because this it taking a lot longer than planned due to changing design, learning the details of systems I only had superficial experience with, and Ubuntu bugs. Originally I didn't have a server or central authentication and was just using Samba to share access the lazy "map to guest = bad user" in smb.conf way. I have IPCop on an old box for firewall, DNS, and VPN. Internet access is via an Ethernet connected cable modem and there's five subnets for my office, household, wireless, public servers (unused), and an isolated one. The isolated network allows me to retrieve user documents from a malware infected system (Windows of course) without it being able to access the rest of my network or the Internet. This arrangement worked for a while but my primary workstation was running out of disk space and I decided to set up a proper network and server to make it easier to control access and synchronize my data remotely. I also plan on building a Debian/Ubuntu repository mirror, public wifi with a "usage agreement" access page like many places have, and a public game server for some Linux games like Tremulous. Nothing really ridiculous but a lot of work as I've found out.
So far about half of my time has been spent diagnosing various problems that often are Ubuntu Gutsy bugs. Not always server-related but it's often hard to tell where the problem is when you're in the middle of a major restructuring and there are a large number of variables. About half have been data storage problems and the other networking.
The storage issues are the result of me hitting the limit of Ubuntu's alternate installer. It's fine for basic setup with RAID or LVM but I had to make my life difficult by mixing PATA and SATA drives with RAID+LVM+LUKS/dm-crypt+pam_mount including encrypted root and swap. It didn't handle that well. I could go on for hours about the problems and other bug reports I filed but more on that later.
Networking-wise I encountered many problems including some of the ones Carla mentioned. Not all were bugs but just design decisions whose basis is hard to understand or track down. The ones we've encountered are by no means all as there are many bug reports at launchpad and on various forums about networking problems that don't occur with Knoppix or other distros. I'm using Ubuntu on most systems so some of my problems are Gnome-specific but many are not.
Network Manager seems to be the cause of a lot of complaints. First, just having the wrong ethernet chip will cause Network Manager to disconnect it for you even if it was working at boot. Or maybe it will refuse to shut down because of it. Then there are the general IPv6 issues. Of course you still have to deal with the normal industry-wide problems like not being able to resolve host names when using a laptop with multicast-DNS (Avahi) active on a Windows network using a something.local domain.
The the link local auto-config emulates Window's behavior but I'm not sure if it's good or bad. On Windows networks I always used a class C network address and if a PC ended up with a class B then I knew that it wasn't seeing the DHCP server and had auto-configured one.
I've had some issues with the host file not being set up properly which seemed to cause a major slowdown in Gnome. It took me a while to straighten it out. The odd 127.0.1.1 entry confused me but apparently it was requested because of compatibility and historical reasons.
For printer configuration I use the CUPS web interface if the graphical utilities don't suffice.
The Bluetooth support seemed to be driven by phone integration usability concerns but it was low priority according to the Gutsy blueprint. The Hardy blueprint has an entry for networkless installation fixes but I don't see anything regarding my drive setup problems, only post-installation management.