Thread Bear,
The PIV based Celerons are low yield crippled PIVs. When the Celerons were made from the PIII this was not a big deal and the performance between the PIII and the PIII based Celeron were very close.
The PIV, do to IMHO the lousy design and the compromises Intel made in order to get the higher clock speeds, it heavily relies on its L2 cache. The PIV based Celeron is a PIV where the die was not good enough to have the full L2 cache and was turned in to a Celeron.
Celeron core is only outfitted with a 128KB L2 cache instead of the 256KB cache present on the original PIV, much less than the 512KB on the current PIVs.
There are a few situations where the Celeron would clearly benefit from a 256KB L2 cache; the two areas that immediately come to mind are general usage/office productivity and 3D games, both of which are in desperate need of more cache in order to gain better performance on the Celeron platform. With that said, the Celeron in its current shape does perform well as a general use desktop processor and brings an appropriate level of performance at a very cheap price.
Still the best price/performance is the Athlon XP line. When talking desktops, for the price of a 2.4Ghz Celeron you can get an AthlonXP 2500+ with a Barton Core, which will run circles around the celeron.
When talking notebooks, it all comes down to what you plan on doing with the notebook, whether you should go PIV or Celeron.
Take Care,
Richard