PCstats has reviewed a 1.8GHz Celeron from Intel :
The Celeron line of processors have always been budget CPU's. With a retail price of just $146 CDN ($99 US) for an Intel processor that's pretty inexpensive. It handles office based work perfectly fine, especially some of the newer software with SSE2 code written in it. If you're strapped for cash and need a low end Socket m478 processor to hold you down, the Celeron 1.8 GHz CPU is a decent choice.
Because the L2 Cache is only half that (128KB for Celeron) of a Williamette P4 (256KB Willy P4), in 3D based applications the performance suffers. As we saw when we overclocked the processor, even at a clock speed of 2.25 GHz the Celeron was unable to beat out a P4 1.6A (512KB L2 cache in Northwood P4's).
Overall, if you're looking for a CPU to do word processing, web surfing, office work, programming or similar work - the Celeron 1.8 GHz will serve you just fine. If you're a gamer or use a lot of sound, or 3D based applications invest in a full fledge Pentium 4. You'll certainly thank yourself later when you're working.