OS X (Cheetah) had numerous problems as Apple were forced to release it when Steve Jobs said it would be, rather that when it was ready.
I found 10.1 not worth bothering with.
10.2 (Jaguar) is a significant improvement.
However 10.3 (Panther) is due out soon and as Apple charges for each new OS you might wish to wait until this release.
I run 10.2 with the 10.2.4 update on one drive and 9.2.2 on another as some pro publishing/design software does not care for OS10.
Overall OS10 is very good but requires some adjustment of approach if you have been with Macs. since OS 6 as many of the bits I want to tweak are now in strange places or are un-tweakable.