For those of you who have left comments asking specific questions about the ongoing Scourge Invasion event, this post over on the official forums might just be what you're looking for; it's a FAQ (frequently asked questions, for you acronym-impaired) all about the Scourge event, that answers just about all the questions we know the answers to so far. We still don't know how long the event will last or what it will take to defeat the invasion, but there are plenty of tips here to get you started on the path. Kudos to player Ghostwalka for putting it all together.
My experience so far with the event has been limited to taking on a few isolated undead in Stormwind & encoutering a Necropolis in Winterspring that scared the heck out of me when I first saw it. I plan to dive headfirst into the events this weekend, though, and this post has me surious to see some of the things that will happen. Check it out & while you're out there battling the Scourge, report anything new you find back here to us!