<p>Do you know any documentation about the rules of using update sites? I have managed the last 2 and a half years the update site of our company, and these are the problems I have to address:</p>

<ul>
<li>Not all projects use the same eclipse version. We had projects that used eclipse 2.1 (WSAD), eclipse 3.0 (RAD 6), eclipse 3.2 (RAD 7), eclipse 3.3 and eclipse 3.4.</li>
<li>The update site of our company mostly packages things together. So I have written litte plugins (sometimes fragements) to package e.g. the configuration of Checkstyle for our company together with the current version of Checkstyle.</li>
<li>We release two times a year new versions of what has changed. So if I have 1 update site or 4, this will change dramatically the load I have to take.</li>
</ul>

<p>So the question is: How many update sites should we use, and if the number is more than 1, how can I minimize the work to do to maintain the update sites?</p>

I suggest to put everything on one web server and deploy the packages for each version of Eclipse to a different URL:
http://your.server/eclipse-3.3/site.xml
http://your.server/eclipse-3.4/site.xml
etc.
This will make it easy to deploy, to keep things apart and it will make it simple for users to see "ah, this is the one for me".