Actually, the thought of all the forumites becoming a singular fortress is an interesting concept. Supposing we maintain free will, memories, etc, since it wouldn't be us if we didn't have those, we would less take orders from some unknown outside source and -decide- to do things individually.
It would probably be rather chaotic, but largely beneficial, because we would not fall prey to dwarven idiocy, unless being dwarves lowers our intelligences quite a lot. Eventually we would probably elevate veteran forumgoers into positions of authority and since they know what they're doing, the fort would be largely successful as long as civil war doesn't break out.
That said, I would probably be content to tuck myself away in the mines and smooth the walls and floors, finally finishing only to begin engraving on them.
I will emerge a fantastic engraver and make pictures of basically anything all over the fort proper so everyone has something to look at other than hunks of rock and soil on all sides.
It'll take a few years, but don't worry guys. You'll all have wonderful pictures of cheeses and heroes striking down elves in all your bedrooms.
As far as the fort on a whole, it would probably be fairly shit for a long time as people settle into the whole world-as-dwarf-fortress thing, learn skills they'll need, construct the fortress proper and the various workshops, tools, and items we'll require, all that stuff. But after a couple years when everyone's used to it, it would be the badassest fort in all existence and would be nigh-unkillable.
Then some ass will breech HFS for shits and giggles, but it'll be okay because all of us will be danger-room'd into supreme fighting fitness.
Even the children.