It still is a fact that buying fast CPUs does only make sense if you

• have rather unlimited funds
• know what you are spending the money for
• and really require highest performance

I guess most of you do not have an unlimited budget to spend for computer components, which is why there are some things to consider before choosing a processor speed:

• Check your requirements!
• 
  If you already know that you are only going to surf the Internet and run office applications, you should even consider the inexpensive Duron. High-end benchmarks like the SPECviewperf usually benefit from a fast CPU, but not the standard software.
  
  
• Games will run best if you team up a mid-range CPU like an Athlon 800-1000 with a fast graphics card. 3D enthusiasts should not pair a Gigahertz CPU with a mediocre 3D-card like a TNT2/Ultra, Matrox G450 or S3 Savage2000. Try to use a GeForce 2 model at least (MX, GTS, Pro, Ultra).
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• The impact of processor price drops is always tremendous, ensuring that your new investment will lose its value rather rapidly. If you save money by purchasing a mid-range Athlon, you still have the option to upgrade to a faster one. Modern motherboards come with advanced voltage regulators, which could easily supply lower voltages (e.g. 1.3 V) for future Athlon cores.
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• Higher clock speeds come hand in hand with more heat, which you have to tackle with a huge heat sink and a powerful fan. The best CPU coolers are partially or entirely made of copper, resulting in formidable prices. In addition, big fans make more noise than smaller ones. Please refer to the recent CPU cooler review .