I think it's important to know what the property (and neighboring properties) look like without snow on the ground. This is important to me and I imagine potential buyers and renters would feel the same.
If you're selling during the winter months, I'd recommend providing pictures of the property in the spring/summer so people get an idea of what the landscaping and neighborhood looks like.
I think I remember hearing something in one of the earlier BP podcasts about @Joshua Dorkin purchasing a property with snow cover then finding out (months later) the snow was covering a lot of trash and terribleness next door.
Depending on your market it's generally harder to rent/sell during the holidays and easier during the summer. If you get someone on board during the cold months it might be easier to offer an extended lease of 1.5 years so they can renew in June (when it's easier to find a new tenant or sell).
Moving between rentals isn't all too much fun, but it's a NIGHTMARE when it's below zero outside. That said, there are always people buying and renting all year. I've helped some friends move at all times during the year. When moving in the winter, the carpet gets pretty trashed because a dozen people are walking in and out of the property with snowy/muddy shoes. Psychologically, the winter moves are a little tougher because there is less daylight, slippery walkways and more clothes (gloves, jackets, etc) for your moving friends to wear. I just get so sick and tired of lifting boxes when it's dark so I'm less motivated to be careful moving heavy items. Totally different story in the summer when it's comfortable, light until 9:30 and you can stop for a "beer break" outside by the truck.
Sorry for the long post.
