We had been running CentOS 5.2 on dozens of our office-desktops. They were boringly stable though little obsolete. Finally I wanted to upgrade my system to the latest v.5.5 so as to use some of the updated packages including Firefox 3.5 and OpenOffice 3. Skipping as much as 2 versions to CentOS 5.5 was smooth as a trademark of the enterprise desktop. There were some minor glitches pertaining to drivers which is documented earlier (CentOS 5.5 Left Me Clueless and CentOS 5.5 USB Device Mounting Annoyance) plus a far critical (purely on the basis of desktop experience) bug that's some way associated with nash and mkinitrd packages.
The latest and great CentOS 5.5 a pig while it comes booting on our office desktops. It stays almost 20 sec at "Red Hat nash version 5.1.96 starting". After booting the systems are very smooth and one could see the advancements of v. 5.5 over 5.2 in terms of updated applications, kernel and other goodies.
Around 20 sec wait is a definite annoyance for any desktop user.
rest here