The lag is a noticeable sticky glitch kind of thing. Seed -7159463857348971439 and the location area (roughly) 449/65/85 - because of the chunk loading glitch in rc1, I had while testing left my render distance at 19 chunks (normally I use 16). When I started seeing the sticky lag spikes I put on F3 and started watching the memory numbers (I'm running 4G allocated to minecraft) and didn't notice anything unusual fwiw.