Yup, as mentioned by several people here already, it's definitely possible to tune a diesel to be quite fast. They make boatloads of torque when tuned and torque is a very important part of the acceleration equation. I'm sure you all ahve seen that video of the 11s 1/4 mile run of that Ford Fullsize diesel pickup. That's a 11s 1/4 for a 5000+lb pickup truck. Surely, a much smaller car that weighs half as much with say, half the power could run about as fast. I'm making assumptions about the Leon TDI, but it's possible.
For anyone who hasn't seen the truck vid, here's the link to the original thread:
http://www.motorworld.net/forum/showthread.php?t=7972 The video link is dead though unfortunately. if anyone has it hosted or knows where to get it, please post a new link.