When I first got up today, I could read/send PMs but not post or reply on the forums. Several hours passed and I realized that noone had posted on the forums for those several hours. At that point, I could no longer PM, either. When people did start posting again, I was still unable to post/reply/PM until I cleared my cookies. So, if anyone is still having trouble, clean out your cookies.
CCleaner is a great, free, safe program for cleaning out cookies, windows temporary files, histories and bad registry entries:
http://download.cnet.com/ccleaner/?tag=mncol
Obviously, the problem here is that the MxO forums don't use genuine home baked Oracle cookies, but the store-bought crumbs-in-a-bag variety.