Since just after fedora 10 was released I've been running a VPS at slicehost. I did 'live' yum upgrades up until fedora 13, 13-14 didn't work and I had to start from scratch.
For awhile now I've felt like slicehost has no interest in being competitive or moving forward since their rackspace acquisition. So here I am thinking I might move to linode.
I've also decided that if I do I want to setup a LTS distribution. At first I considered CentOS because I have only ever used redhat/fedora. The problem is I'd like somewhat newer software (but it doesn't have to be bleeding edge). From what I've read it seems ubuntu server LTS is the way to go in that respect.

So on to the main point. I've never used a debian based system. I know the package manager is different but that seems fairly straightforward to figure out. I guess what I'd like to know is am I in for any surprises besides that?
Currently I have apache installed with mysql, php, modssl, modperl, and a few other small addons. I fully expect I can muddle through installing all that with apt, I'm guessing a different file/folder setup but nothing big (I hope). I also have a bind primary server setup.

My concern mostly resets on my email setup. I'm running qmail-1.03 using a large set of patches (including the netqmail changes), some domainkey/dkim patches, and also SSL/TLS. I've compiled spamassassin, vpopmail for a checkpasswd/virtualhosts, and dovecot for a pop3/imap server. I really don't remember all the libraries I needed to compile all of it, I think most of them were installed using yum's "Development Tools" group, with a few extras I had to install. In fedora I also had to setup a 'fake' SMTP rpm to satisfy SMTP dependencies, any ideas if I'll have to figure out how to do the same on ubuntu?

Any comments/suggestions are welcome and appreciated. I have considered trying a new smtp/pop/imap setup but for now I think I'll stick with whats familiar, and perhaps later I will test something newer out.

One piece of advice I'd offer is, avoid compiling anything whenever possible. Unless you're using Gentoo, compiling things yourself is a recipe for disaster, since few people who install from source update as often as they would if they were installed from packages; updating every package on your system is as simple as "aptitude update && aptitude upgrade" (or apt-get, or whatever you use). Compiling from source also may not get backported security fixes that the distro provides (unless you compile from the distro's source packages).

Beyond that, I can't offer much advice with a mail server, sorry.

There are centos repos out there that provide newer versions of packages.

I see where you're coming from with that. I will likely try to use spamassassin and dovecot from the repo, though last time I tried dovecot2 the vpopmail plugin wasn't working, but I could give that a shot again.

For me, moving between YUM and APT isn't all that hard. Harder is init.d and the way different locations and names for the various server configs. Luckily Google is your friend.