TheRooster

I ran a pair of the old style Falken Azeni's for about two years on the street. Put 40k on them, had no problems. Of course, I wouldn't dream of Autocrossing them, but they were really decent street tires. I'm now running RT-215's, and again, I would buy another set of tires if you plan on taking to the track, but as far as street driving goes, so long as you don't jackass it, they're quite capable. I've driven through rain, dirt, gravel, you name it. No big problems.

I think the key point to be made is: If you plan on autocrossing, you ought to have a set of dedicated autocross tires.
Having two sets makes both of them last longer, obviously than if you simply had one set for both.