What load balancing software do you use ?
SwellJoe: I've used pen, Squid, and LVS.  All useful for different situations, though LVS is just not practical for the vast majority of situations.PerlBal looks really cool, as being written in Perl means it has some of the same kinds of flexibility that Squid has (a good reason for Squid is that you can write your own balancing algorithm in any language you like in a redirector script--I always used Perl, or Python when I was working with the Zope guys--so, you can actually do crazy stuff like choose the right server based on keeping them "primed" for the content users are asking for based on URL, or you can use destination URL hashing and achieve the same effect even if you have millions of URLs).  Squid also has experimental support for ESI (Edge Side Includes) which is pretty awesome...build a page from disparate and wholly unrelated servers using a simple templating system, and caching them.  I don't think any other Open Source product out there has ESI (experimental or otherwise).