id say hes a pretty good driver who drives rather hard, a lot. in some of his earlier (i dont know about lately, i havent watched/read recently) video blogs he used to post track day videos and talk a lot about his ultima gtr.
that being said, most of the cars he buys arent meant to be driven nearly as much as he does.
http://www.autoblog.com/2012/09/13/jay-leno-drives-worlds-highest-mileage-lamborghini/ - a 1967 lambo 400gt with 250 000+ miles
http://jalopnik.com/5559767/i-sold-everything-to-buy-a-lamborghini-and-drive-across-the-country back in 2010 over 100 000 miles on it, before that, one of the highest milages seen on a lamborghini for sale on ebay motors was about 38000, yet most arent driven/accumulate much more than 10000 miles
that being said, he definitely drives them hard, and the reason he always seems to be running into issues isnt necessarily him driving TOO hard, but that he has driven hard for so long.
it would be awesome to see jon on top gear, either as a siorpc, or some sort of challenge/feature with his r8 or one of his other cars