Have you been getting a lot of invites for WLM recently? This is due to the fact that Microsoft has recently been updating their service system. They have been giving out a large amount of invites so they can test whether the new system can handle the 180 million+ users on MSN Messenger.
Microsoft recently hit their first target number, so they decided to give out more invites so they can hit their next target number. Giving out more invites makes sure that more people will join the beta, and will also help Microsoft test their servers for stability.
On that note, there are still many people who want to join the WLM Beta. Microsoft has opened up its WLM service to anyone who wants to join at the Windows Live Ideas Homepage. However, there is a catch. Once you sign up for the beta by scrolling down, and clicking "sign up", you won't be able to automatically be able to use WLM, but be on the list for an invite on Microsoft's next round of invites.
The exact date of the next release is still unknown, but Microsoft promises us to give out multiple releases this year.