Speaking from my own experience, i think 10% is far too low. I purchased my mk6 in sept2010, and secured a 2.5K discount on a 27K car. 9.25%. This is a built to order spec.
I have also just ordered a new mini conv for the other half, secured a 14% discount.
For me its all about waiting for the right deal, dont be fobbed off with the deal of the day/week/month chat, theres always( almost) a better deal to be had. Sales guys are under extreme pressure to meet targets.
The buyers who pay more,

pay for your discount................................