After the initial release there will be a large number of bugfix releases, probably on a daily basis until things have settled down.
I also don't really understand why the save incompatibility is such a big issue. After all, how long do your fortresses really last? Between nobles, tantrum spirals, and magma, most fortresses to crumble to their doom relatively quickly. Most of the fun of a fortress is also at the start before you're well established with an army of legendary wrestlers able to kung-fu a megabeast to death in second.
Toady creating the motto 'Losing Is Fun' because he didn't want people to play the fortress, he wanted you to play the world. That means that even if the fortress falls, he wants you to start a new one in the same world(or reclaim the old one, provided it didn't have magma...dang magma reclaim bug). So you saves should last a good while for each world...you aren't REALLY creating entire world, completely with history, and then playing one fortress before throwing that world away, are you?
And more on topic...this sort of thing is far from the only thing left. In the Remaining Items thread, that last section with nothing greened out will take a couple weeks
if we're lucky. Probably longer. Think of it this way, having patience gives a good product. Having haste gives you an EAGames style gigantic amalgam of bugs that barely resembles a game(I'm looking at you, SimCitySocieties).