The Atlassian eclipse Jira Mylyn plugin directions are somewhat confusing. fro eclipse 3.5 you need to use the non-weekly update url of:
http://update.atlassian.com/atlassian-eclipse-plugin/e3.4
For Eclipse 3.6 which has Mylyn 3.4 and not Mylyn 3.3. you need to use the weekly update url of:
http://update.atlassian.com/atlassian-eclipse-plugin/weekly/e3.4/site.xml
but on that page there is no mention of this, I guess we are suppose to be mind readers.