I'm pretty sure livvie meant something totally different (like Blizzaks or Michelin X-ICE) for winter tires. The Sumi's are NOT all-season, and therefore likely quite poor in snow. If you get ANY snow you must drive in in the winter, I'd be iffy about using a summer tire then. Traction will not be good. Rain and/or cold is no problem, but snow is another matter. That said, some people *get by* with summer tires all-year-round. All-season tires are (of course) better for this purpose, but compromises are made to achieve all-season.
Summer tires typically have better traction, wet & dry braking, & cornering abilities than all-season tires.
True winter tires (Blizzaks, X-ICE) are vastly superior to all-season (and summer) tires in snow and slush.

Getting a totally separate set is not really more expensive over the long run, other than getting a second set of wheels to mount them on. Many people do the steel wheel thing, or even buy inexpensive alloys for the winter set of tires. Road salt and slush take their BITE out of rims in nasty winters anyway. Let it eat away at cheaper rims!
Storing the out-of-season set of tires/rims can be an issue, however.
Some people opt to swap the tires on the same set of rims, but that's hard on the rims, and gets expensive (mounting & balancing costs). Plus you still have to store the out-of-season tires. And the single set of rims are at the mercy of the winter sludge and salt.

Steve

STOP terrorism - Drive a HYBRID

Vehicles:
350 miles a week ------------ 2006 HCH II, Magnetic Pearl, w/NAVI (born on May 25, 2006)
350 miles a month ---------- 2003 Mazda Tribute ES-V6
350 miles a year (for now) - 1986 Mercedes 560SL