yamadooed is all over it. MI requires you to buy a trail sticker- whether you're registered in MI or not. So even MI residents who have their machines registered there, still need a trail pass. WI says you don't need a WI trail pass, if registered in WI. So yes, lots of us go ahead and get dual registration b/c it's cheaper. $33 for two years, vs $35 trail sticker good for only one year. If you live in IL and want to ride in IL, you must be registered here. It's $18 for 2-3 yrs, peanuts if it means they leave you alone when running the Chain for fun. If you live elsewhere, you at least have to be registered somewhere- to ride in IL. We don't have a trail sticker.
You have to pay sales tax to register in WI. For most people- you've already paid it. And unelss whereever you paid sales tax- that rate was less than 5.5%, you're set. Just note that it's been paid (I've registered 4 times in WI and just said I paid, and never submitted proof- but I really did pay- just surprised I didn't have to send anything). Only thing I"m not sure on is the sales tax for private party/used machines in IL. I know for boats, you pay the tax no matter what. I thought snowmobiles moved to this as well, but maybe not. I'm sure they will though.