Geez, guys, let me straighten you out !!
The new and old Athlons and Durons are better than the P3's at "professional" applications with OpenGL, CAD or other FPU-intensive applications.
When it comes to the apps most of us use day to day, the new Athlon (Thunderbird) is just marginally better than a P3 Coppermine, generally speaking, but it's not enough to switch platforms for if you already have a P3 compatible mobo. The Coppermine is significantly faster than the old Athlon - close to 10% on most benchmarks - and the old Athlons come only in the outdated Slot A format, not Socket A. The Durons are close to the old Athlons in performance and come in the Socket A format like the new Athlon/Tbird (thus providing a nice upgrade path, since they're interchangeable). The Celerons are great overclockers, but on benchmarks even then come out inferior to the stock Durons and Coppermine @ around 600 MHz.
The only time that an AMD CPU was superior to an Intel was for a short period in 1999 when the now old Athlon came out and bested the then P3 Katmai (now almost unavailable) by maybe 10%. But Intel responed quickly in about 2-3 months, regaining the performance lead with the Coppermines with on-die cache, something it took AMD about 9 months to duplicate.
The real claim to fame of AMD'S CPU's is that they are cheaper, not necessarily better, and they put competitive pressure on Intel as to both performance and price.
This is my good deed for the day.
P.S.
And yes. P3's are generally better overclockers than Athlons, even with Golden Fingers Devices.
But these are all generalizations.