No, I havn't had a leak on an R-410a system yet. The 3 or so leakers I have found have been over a 10 year period since I started doing service.
We are a 2 man shop, so we don't have a whole heck of a lot of systems out there. At 200 installs a month, you guys put more in per month than we have in 4 years.
I imagin as everything changes over to R-410a more in the next few years, we will all be spending a lot more time finding and repairing leaks. There won't be any more of the juicing a pound or 2 of refrigerant in a system every couple of years. Those little small leaks that add up to a pound or less a year in an R-22 system would make an R-410a system go flat in a matter of weeks.
Smaller molecule + higher pressure = faster leak rates.