I first tried siping on some Toyo all season tires on one of the Taurus sedans, as with 50k miles they were starting to move around more in the rain filled grooves created by the studded tires around here. It helped a lot as the siping was a bit sparse to begin with, and I ended up getting 70k miles on the tires. The newer versions of the tire appear to have more siping.
I have four seasons now on some Michelin Artic Alpins, I take them on and off as needed during the winter to try to save tread, and have ended up leaving them on for a couple of months at a stretch. They're a low temp compound tire with lots of siping, and except for tire life make decent all season tires. They don't work as well as studded tires, at least compared to some Goodyear Ultra-Grips that I ran for eight years on a Honda Civic, but are better than regular all season tires in snow and ice.
I hand siped the fairly new Michelin LTX A/S on my truck, as they're pretty bad on ice and were even a bit goosey in the rain. I just extended the existing sipes and added a new row of siping on a tread block if the spacing warranted it. It has helped in the rain, but I still needed chains on ice. Note that I live on kind of a steep hill and the ice got pretty bad this last winter. I watched a 4wd Jeep with Goodrich AT tires, which have a severe snow rating, stall on the hill in front of my house and start sliding backwards. He managed to use a curb to turn it around and go back down at least pointed in the right direction. 4wd pickups were getting sideways going down the hill. Next year I'll get some studded tires.
