Hit it with PB Blaster and it soak for awhile. 
Loosen the nut until its almost off then try to turn the bolt. 
If it doesn't want to turn then jack up the frame near the back while trying to turn the bolt.
Usually that will take tension off the bolt then it will turn. 

Once you get the bolt turning, spray some more PB in there.
Put a socket back on the nut with a short extension and lightly tap it while twisting the bolt back and forth.
If you have reduced the tension enough,  the bolt will slide with minimal effort.

Nutec bolt-off works a lot better than PB.
If traditional methods don't work, call up a friend to help.
You'll need an impact wrench and an air hammer.
Install a pointed bit on the air hammer (like a center punch) and then position the bit directly over the center hole of the bolt on the nut side.
Use the impact wrench on the other side to turn the bolt while the air hammer is pushing the bolt out.
If the quad is on a stand without anything else holding the swingarm on or you're some kind of spiderman/stretch armstrong lovechild you can do both at the same time.
It takes a good amount of time to really get it loose enough to remove, and you may have to use a long center punch if it gets hung up halfway through.

Would probably be a good idea to replace both the swingarm bolt and the bearings if it's that difficult to remove, but at the bare minimum at least replace the bearings.
The reason I recommended using the center hole on the bolt is just in case you somehow can't remove it, or the bolt itself is fine once you get it out...then the bolt isn't a completely lost cause.
Repeated bashing against a nut covering the threads of the bolt will still damage the threads, so try to use that as a last resort.

I pulled all the other mounting bolts, using a socket wrench I could pivot the motor on the swing arm bolt. So it's stuck pretty good. Gonna need to soak for awhile. Thanks for all the suggestions gentlemen...I hope I don't mushroom the end of that bolt!

Yagerzzz on the old site said that he drilled the bolt all the way through with a bit just a tiny bit smaller than the bolt diameter.
Said it was thin as a beer can in spots, but didn't damage anything other than the bolt itself.

Yeah I was thinking that if I F up the bolt I'll be drilling right up to the engine case bushings. Oh what fun that'll be...   

I soaked one with penetrating oil, removed the nut, had a friend turn the bolt while i took an old Philips and put it in the small hole on the nut side and hit it with a hammer.  Came right out.