Tazer: Ubuntu is built on Debian so you get all those benefits plus Ubuntu updates the software in it's stable repos much more often than Debian (stable that is). Btw you can update any distro as often as you like, fex. on Gentoo just create a cron job that runs
emerge --sync ; emerge -uvN world daily or whatever.
Solaris was hit-or-miss when they first went x86 but I guess with their opteron offerings they should have sorted that out by now. Still most people I know prefer a GNU userland and Dr_Bend_over has experience w/ Ubuntu already so no point changing just for the hell of it. Honestly, it's not much to brag about anyway. If lineage is important for some reason or you prefer a BSD userland than FreeBSD or OpenBSD would be my choice for a server. Solaris is nice with ZFS and all but I'd leave it on Sun's machines. If bragging is important than you go with LFS or plan9 or something more obscure.