Quote...Event begins Wednesday, August 4, 2010 at 11:59 p.m. Pacific and ends Monday, August 9, 2010 at 10:00 a.m. Pacific.
Eligibility Requirements
If you have ever applied a Retail Product Key for Star Trek Online to your account, you are eligible to participate in the Welcome Back Weekend. All you have to do is patch up and log in.
"Patching up" will include the Season 2 update and some post update patches. Download early!
The FAQ says that demo accounts are still subject to normal demo restrictions, so if you haven't ever paid, you don't get unlimited play.
Oh, I should mention that there are patches to to the PvP queue system. It's not a total overhaul (yet), so I can't say how improved it is.