As some of you may have noticed (and thanks to those that notified me of the errors), the site was down for two days, the forum had errors, the playground was 404 
This was due to a server change I requested because of frequent downtimes on the previous one. However, the new server my site was moved to had certain features differently configured – that rendered my site inaccessible.
First was the php version, that made my WordPress installation go AWOL (had to switch from php 5 to 4 to have it work). That also lead to errors on my forum pages, but those were corrected using some tips from the bbPress forums.
The cause of 404’s on my playground folders was that my .htaccess for that folder used the directive SecFilterEngine Off, in order to disable mod_security (which, when activated, interfered with my Ajax calls). But on this particular folder, mod_security wasn’t configured and thus the .htaccess generated an error and wasn’t correctly interpreted (I used it to disable mod_rewrite in the playground folder too, in order to prevent WordPress’ rewrite rules – but since it had an error in it, the default WP rules were applied and no such page was found).
On a happier note, I just launched the “splash page” of an upcoming community website I’m working on, the one that pushed me to write the code for the vertical kwicks.