We just finished a week of hell after trying and failing to upgrade from Debian Lenny to Debian Squeeze. None of the Debian Linux kernels working correctly on our stock Dell PowerEdge T605 hardware was the first major headache and KDE 4 was the second. In our 10 years of using Linux its user unfriendliness seems to be as poor as ever.
With the latest KDE 4, it seems that KDE itself has also gone from bad to worse. We migrated from Gnome to KDE many years ago because we found Gnome to be buggy and user unfriendly only to discover that KDE was only superficially stable. KDE 4 takes this to a new level and our log files are filled with records of segfaults. KMail was once riddled with serious bugs but these were ironed out in KDE 3 and it became a usably-stable e-mail client a few years ago and served us well. Not so with KMail from KDE 4, which regularly segfaults, losing and/or corrupting data and has consistently failed even to move significant numbers of e-mails around within its own Maildir.
Following our catastrophic encounter with the latest round of open source software we have decided to migrate everything from Linux+OCaml to Windows, .NET and F#. Unfortunately, KMail quickly threw another spanner into the works because it is almost entirely incapable of exporting e-mails to other usable formats. We eventually managed to migrate essential e-mails by setting up a local IMAP server using dovecot, painstakingly copying a few mails at a time from KMail's local store to the IMAP server and then downloading them using Microsoft Outlook. Any attempt to copy a significant proportion of our 3.2GB of e-mails resulted in KMail either crashing with an error after it had corrupted its own file store or dying completely with a segfault.
Back in 2007, we were reluctant to adopt Windows due to previous bad experiences but this latest round of failures is the last nail in the Linux coffin from our perspective. Goodbye and good riddance, Linux!