I have a few models in my build queue that have rubber tyres - aselection of half tracks and armoured cars in 1:35 and a 1:16 T-34.

What do you guys do with them.

Use as is
Scuff up to take the shine of them
Paint them

Cheers,

Nigel

Nigel,
"Rubber" tires on kits can be a double edged sword-- they can look great or terrible, and sometime they can be a real problem. Real rubber in a kit can have some unfortunate consequences as the chemical compounds in the rubber can either deteriorate and crack, or it can attack the plastic. Fortunately, most mainstream model companies today have changed their formulation to Nylon based compounds, which don't have the same effect as they used to. As for "weathering" a "rubber" tire, I like to run them over a sheet of 400 grit sandpaper to give them a slightly worn look, and a little heavier wear on the tread. I do this for race cars or military vehicles. On vehicles like tanks, it really depends on the amount of wear you add to the tank--brand new tires are going to look odd on a heavily worn tank--I actually prefer to "gouge, chip and cut" tires on my tanks-- as a former tank commander, I really never saw a tank without several tires that were slightly gouged or chipped--even fairly new vehicles-- they just don't stay new for long. A brand new or nearly new vehicle is an exception. I usually use acrylic paints on road wheels or wheel hubs on my models-- since acrylics are less likely to interact with the material of the tire, although I have a kit that's over 50 years old with Nylon tires and enamel paints on it that has never had a problem--the old Monogram Jeep and 37mm gun.
VR, Russ