there are some news about the invite system over at the oneplus forum:
Update 3 (May 9, 2014): There are a few commonly asked questions regarding the invite system that I can help clear up:
How do I get an invite?
The main method of getting invites will be through others. In the beginning, when not a lot of other people have the device, you'll be able to get invites through contest and raffles. We have planned ways so our early fans, as well as people who weren't here from the beginning will be able to obtain invites.
When do the next batch of invites roll out?
The first real batch of invites roll out late May, and will be of the 64GB Sandstone Black version. Any invites that you might have been promised before this, will be sent during this time.
How long are invites valid for?
For invites that you receive, they are typically valid for 24 hours. If they expire, they get returned to sender so someone else can get a chance to buy it. Alternatively, you can ask for the sender to resend it to you. For invites that you can give away, they are usually valid for longer, usually 1-2 weeks.
How many invites can I give away?
This varies. In the beginning, the quantities will be smaller, but increased as time goes by. You will frequently receive new invites to give away as production ramps up.
When do I receive invites to give away?
You do not automatically receive invites when you purchase a phone. We will need to manually roll them out according to our operations situation.
Hope this clarifies some things.
Just as a reminder: If you are looking for invites, please post in this thread!