I've been running AMD hardware since 1994 or something. The only
problem AMD used
to have was floating-point speed. Games
suffered, so Celerons sold much better than AMD-K5/6's. However, in my
experience, I've always had faster 'desktop' (read Word, database,
etc) performance. The new Athlon/Duron cores do have very efficient
FPUs, so games run excelent on AMD hardware (if that is your poison).
A part of the reason for that is the cheaper CPU allows you to buy
more RAM. I had twice as much as my friends :)
On the remark on Athlon out performing the P4 at the same speed, that
is mainly processor design, the P4 has a 20 steps deep pipeline, the
Athlon has 7 or 8. A deeper pipeline gives you higher clocks, but also
a higher price when a branch prediction failes.
If you really want to see good writing on CPUs go to arstechnica.com, 'Hanibal' knows what
he is talking about.