Overall I'm liking what I'm seeing, a few random points to do with both features and devcycle. Maybe some of this is in the works, or isn't part of DF's design philosophy but the occasional newbie perspective is still useful to ensure the end product isn't impenetrable to non-veterans.
1. Bugfixes, bugfixes, bugfixes. I understand that .31 is very new and Toady's just one guy who I assume has a day job, but some of the bugs are extremely frustrating and as a new player I don't really have any interest in 40d. I guess what I'm saying is I hope Toady keeps his eye on the ball and doesn't get distracted by side projects--owing to the nature of DF I'd rather have fewer features that all work as intended than a lot of hacked-in stuff that looks cool but doesn't work right.
2. The ability to only have one extant fortress at a time is very annoying, as is the inability to quit without saving. Owing to how easy it is to save off files and how the current system is implemented, I can only conclude that this is a design decision and it isn't a good one. Aside from playability the trouble of having to copy over one save at a time makes it difficult to isolate bugs and quirks. As for what I'm assuming is the long-term desire to let players build many forts on the map I would say go with Simcity 4's non-temporal system. Making sure neighboring forts A and B are the same age looks good on paper, but the ways of enforcing this tend to utterly kill gameplay.
3. I'd like some kind of a newbie-mode option in the ini, or at embark or something to block invaders and severely nerf wilderness threats for two years or so to give people who aren't ultra-hardcore-familiar with the game mechanics some time to get their surface constructions and upper fort going before worrying about serious threats. A lot of people I've talked to have said one of the reasons they couldn't get into DF was they got hella murdered by goblins before they could even figure out how to grow food.
3a. Tone down immigration and wealth triggers. A couple of successful artifact jobs seem to be capable of generating enough wealth
to trigger tons of incoming dwarves (which the fort can't handle yet) and spawn all sorts of nasty hostiles that shouldn't be showing up until the player has developed a proper infrastructure. Losing may be fun when magma is involved, but trantrum spirals and overwhelming invaders are just lame.
3b. Nerf tantrum spirals. I want to lose because I dug too deep and/or flooded the fort, not because the RNG hates me.
4. Owing to my status as a newbie, it's time to piss off most of the veterans.

The ASCII UI is interesting, but it's hard to make things out and it just isn't all that visually appealing. Frankly there's a reason developers moved away from straight text as soon as the technology became available. The tilesets on the other hand do a fine job, but they're limited by the standard output and doubling up with plaintext characters causes UI problems. Perhaps for one of the next major releases Toady could look into revamping the UI so it spits out just an array of tile structures (the game map), which are then run through an I/O module which also kicks back the player input. In the long run it would probably save work since Toady could effectively draft the tileset makers into making the game look and feel good (i.e. the current clunky key-combo input becomes their problem) while he focuses on doing awesome new game mechanics. ASCII could of course be one of the options for the old-schoolers.