WoW 4 will be back 'soon'. Blizzard has a bad track record for bringing servers back up on time when they reserve 24 hours for a shutdown. Use your downtime to get your addons up to date (where there are updates). The update sites are going to be hammered hard once WoW is back up.
I will be starting with a clean slate for addons. We get a lot of crap over the years, and a new version is a good time to clear it out. Others may prefer to wait for Cataclysm, or not clear out at all.
- Backup your addons folder. On my PC this is in C:\Program Files\World of Warcraft\Interface\AddOns. I will move everything that does not start with Blizzard to a new folder in the interface directory : Addons-3-3.
- Move your WTF folder. On my PC this is C:\Program Files\World of Warcraft\WTF, and will be renamed WTF-3-3. This is where all your customisations are held, including where addon 'Save' files remember data when you log out. Also, if you feel the need to backup data in case of data corruption, this folder is the one you want.
One of the first addons I will be looking at is the QA3 successor : Auction Profit Master (currently only on WoWInterface). I have no idea as to the quality of the addon.
Even with QA3 I will be looking at Auctioneer. I can not find an update, but I would be astounded if it is not updated. I like it's pricing history and other features, even if I think that pricing will be unreliable over the next few months. I am uncertain what will become of auctioneer, with it's author citing it's financial status. Edit: There will be an update (Auctioneer Forums)
Curse has a page for addons that authors feel are Cataclysm compatible. Caveat Emptor - these are new days, and there will be bugs.
New bright shiny distractions. Players wanting 9 glyphs instead of 6, with some of their existing glyphs being charred or repurposed. Post your auctions however you can, at higher prices than we previously had, and watch the profit roll in.