I was just up in the southern part of the wilderness (Lake Creek valley/Ashnola Pass) this weekend. This is a couple valleys west of Thirtymile/Chewuch (on the same road) and smack dab in the middle of the area burned in the 2003 Farewell Creek fire, so conditions might reflect what you'd see in other burned areas. I haven't really written up a trip report, but here's some (hopefully useful) information about current conditions.
The lower section of the Lake Creek trail is somewhat used (we saw a couple day hikers) since it leads in 4 miles to a lake. This section is a little brushy, but the footing is fine and it's very easy to walk straight through the brush that hangs into the trail. All downed trees from last winter are already cleared in this section. Above the lake, however, the trail is much less used. The brush is thicker, and there are lots of downed trees of all sizes across the trail. Some of the snags presented interesting problems to solve. Nonetheless, the trail surface was in very good shape. Personally, I kind of enjoyed the adventure, the solitude, and the feeling that no one else had been through in a while afforded by the subpar trail conditions (keeps the riff-raff out!), but with a heavier pack or stronger sun (we were shaded or clouded for most of the day), it could get miserable.
Some photos and video.
There was plenty more brush than was shown, but overall, we spent much more time just walking than climbing over stuff.
Also, see the USFS conditions page (links for each ranger district, you want mostly Methow North, maybe Tonasket) and the more static trail descriptions (some of which describe burn/maintenance status).