I'm thinking of getting a shed or something to keep it outside -- I'll try and ride a bit on my CB500 over the winter, but because I don't commute with it, I don't think I'll be giving it regular rides (I do ride my bicycle through the winter ;0).
Anyhow -- I'd guess a big reason to keep your ride inside during the winter are the thermal issues that come with winter -- freezing, unfreezing, etc. Is keeping it in an unheated shed not much better than keeping it under a regular ol' cover?