Both architectures are x86-based, but represent significant changes in how AMD is designing processors. Bobcat is AMD's new mobile platform and Bulldozer is focused on servers, each branch away from traditional designs to cater to their specific markets. Bobcat, for instance, will feature extremely low power requirements, with thermal envelopes under a single watt.
Without revealing too much information, the company specified that performance was not sacrificed as it often must be on most ultra-low power processors, claiming it is within 90% of modern mobile processor range. Clock speeds, pipeline depth, specific instruction support and other details were left out -- aside from mentioning that they will fully support SSE1, 2 and 3.
The new CPUs should appear in 2011 -- which gives Intel ample time to adjust their own lineup, so there's no real way to determine how they well respond. AMD made huge waves when they pushed out the (arguably) revolutionary X86-64 instruction set in the K8 architecture. It was one of the few times that Intel ended up following AMD, and marked a point at which AMD held a respectable command of the CPU performance market.
That hasn't been the case for some time, and clearly AMD thinks that radical engineering is the solution. Though it's more than a year away, it's still very exciting stuff.