Registration is back up. It looks like the post requirement to see the vendor section is equal to or less than 20. They're still working on it to see what works.
If you had an account that got purged: Pretty sure it's gone and you'll have to make another. Unless you were a big member/vendor of some kind. Then I'd try messaging the mods about it.
If you join: It's a form and community that happens to be a market. Not the other way around. The mods/forum doesn't even get paid for the orders. Speaking of! If you appreciate them, there is a stickied thread with a bitcoin wallet you can donate to the costs of running the forum :-)
How quickly will I get deleted again for little activity? I have other things to do than post a lot of replies.