[Taeric]

Celly Ds perform well for the price (2.93s go for around $75US), but they're not on par with P4s. They're not targeting the same users, though, so you really can't expect similar performance. A Celly D will handle any type of routine application you throw at it without breaking a sweat. They can handle games as long as you're not looking for high/extreme settings and killer frame rates. They're fully intended for the budget market and serve the needs of that market well. If you have the budget and need for a high end machine, this isn't the CPU you want.

And yes, Celly Ds are considerably better than their predecessors. A 1.8 GHz Celeron is based on the Williamete core as bigval said, and that was not one of the better products that Intel put on the market (I have a P4 1.5 GHz Willy at work, and it doesn't exactly burn things up). Celeron Ds are based on the Prescott core, which although it produces a lot of heat, is a solid core.

 

[Taeric]

AMD and Intel CPUs perform different numbers of operations per clock cycle, so clock speed on its own is meaningless. You can roughly multiply an AMDs clock speed by 1.5 to get an Intel equivalent, though there are lots of other factors that determine performance. So yes, a 2.0 GHz AMD will destroy most 2.0 GHz Intel (with the exception of the Pentium Ms). Those are different generations of CPUs, though, so you really can't expect to draw a comparison between them. A 3.0 GHz P4 is similar to a 2.0 GHz AMD, though not exactly equal by any means.