I finally decided to upgrade my Ubuntu Server 6.10 install to the latest version, 7.04 (Feisty Fawn). Out of habit, I now wait a few weeks before upgrading to the latest version of anything to ensure any last minute bugs get worked out.
Best of all, I upgraded the entire OS remotely using SSH. Upgrading your OS remotely is usually not a good idea, but if you know what you’re doing, go for it! Ensure you backup any custom/modified configuration files just in case you press a wrong key during the upgrade! 
The upgrade worked well, with the exception of recompiling eAccelerator (to work with PHP 5.2.2) and updating a line (see below) of code in WordPress to make everything work smoothly.
Immediately following the upgrade, I noticed that my WordPress blog was loading very slowly and I also noticed random strings of hexadecimal characters at the top of the main blog page.
If you upgrade your server to Ubuntu Server 7.04 and run WordPress 2.1.x, ensure that you change line 832 in wp-includes/functions.php to the following (all on one line):
@header($_SERVER[“SERVER_PROTOCOL”].” “.$header.” “.$text, true, $header);
Once you make the above change, your blog should load normally.
Update (5.15.2007):
With WordPress 2.2 (released today), the aforementioned WordPress fix is now irrelevant.