Wombats are the animal kingdom's answer to a bulldozer. I've mentioned before on a Mudcat thread the two occurrrences I've witnessed where a wombat and a vehicle had an exchange of courtesies.
The landrover had to be jacked up to release the wombat from under the diff; it ran off as soon as the vehicle's weight was lifted but the diff was cracked. The VW Karman Ghia had the right side front wheel assembly pushed back about 2" although, again, the wombat ran off.
JennieG's comment about them making poor pets is only mostly true. In NSW the equivalent to Queensland's Australian Wildlife Hospital is WIRES (Wildlife Information and REscue Service) and is composed of groups of volunteers all around the state. Many marsupials come into care as orphans still in the pouch and are raised to adulthood and released into the wild. Orphan wombats are really affectionate as youngsters but, as adolescents, their affectionate behaviour includes biting their mates on the bum. A wombat's bum has rather tough and thick skin and tolerates such affection rather well but your average human leg is more sensitive and fragile so, at this stage, wombats in care are transferred very much to the outdoors. Where their liking for burrowing and bulldozer abilities don't endear themselves to the average householder.
Koalas, on the other hand, will only piss on you when you pick them up and hang on to you with fingernails that are designed to grip onto smooth and tough manna gum (Euclayptus viminalis) trunks and similar.