Chad posted a comment about the upcoming 4.0 AH changes, where every posting will need a hardware event. This is likely to break QA3 and Auctioneer in 4.0, at least temporarily. My guess 4.0 hits first week in November, others guess next Tuesday. I had one guildy sure that it was dropping last night.
Come 4.0, the demand for glyphs should be astronomical in the first week. The demand for some gems will be 'very very large', as players juggle the new stats. The enchanting and leg armor markets may also experience a smaller 'spike'. There should be a large increase in alt's running dungeons, so levelling enchanting supplies should get cheaper. I will be adjusting my prices to match my expected demand. I am more worried about selling out of glyphs than I am about being undercut.
Change happens. Market rules change, both in real life and in WoW. Anything computer related can break at any time, including your PC, WoW itself, and our addons. It hurts when it happens, but you should always have a plan. The better prepared you are, the better your profit. Some of your competitors may even drop out for a week untill they get organised.
On day 1 of 4.0, I fully expect that our addons will be broken. I will be starting with a clean slate, starting with a default UI, and adding addons back in on a case by case basis. I will attempt to have a full set of auctions posted before each shutdown, on a 48 hour posting, but this is business as usual.
In the worst case scenario, become familiar with the default auction posting methods. It is slow, but works. It is more important to be on the AH than to be the cheapest on the AH. Other posters will also have problems.
Watch for updates for the addons, both QA3 and Auctioneer. Look at their forums. Offer to help. This can be taking part in an 'alpha' release (bugs and all), assist with the programming (a lot of student/professional programmers play WoW), or by cash donations. It is always easier to use someone else's work, but sometimes if you want something done, you have to /assist