Given my low amount of available play time, I've only just now gotten the shop set up enough with an MFSU and some power generation (and a lot of redstone 2 wiring to control it all from switches). I've also collected about 250 buckets of oil that I was planning on refining to set up a combustion engine. And I finally started work on an industrial blast furnace. To lose it all will be a bit disappointing. I was trying, this world, to make everything myself rather than use someone else's shop like I did on the last FTB server, but I probably won't do that again if the servers will be changing a lot. I'll just be that neighbor who borrows your tools over and over again (right, MD?).
Not all of it was a waste, though. I learned a lot about redpower 2 stuff as well a little bit of the xxycraft tanks and power converters, so every bit I learn will speed things up on future builds that include those mods.
I could live with a constantly changing world, but my focus will have to shift from building to just getting enough resources to explore a lot, while building stuff on other folks tools/tables/etc.
I personally prefer a more stable, long term world as it suits my casual play, but I can certainly see how popular the IAF world is due to folks wanting to try new things when they play out the old. Given my schedule, a two month cycle would give me 30-40 hours of play time on any given world, so I would just have to be careful how I spend that time.