The first thing to do is find out what program or programs are using most of the cpu. I run top in command line in these cases and the solution usually suggests itself once you know what is going on.
I also run Gkrellm on my desktop to keep tabs on the health of the OS and it usually gives a heads-up when something is not playing nice. Gkrellm is installable from the repositories and is very configurable, and uses krells as well as bar graphs. Some people like Conky because it can be made to look pretty, but Gkrellm with default theme is very functional:
I particularly like how Gkrellm uses different colours for the CPU graph - brown for system, blue for user, and green for applications with very high nice levels (usually daemons that use a lot of CPU but give it back when system or user programs need it.) Also, disk, memory, and network reads are in blue while writes are in brown. Neat.
I have noticed on my new 12.10 64 bit install that Firefox has been hogging the CPU on occasion, but I will be installing 32 bit on this faster dual core machine to see if the problem persists.
I've also noticed that 12.10 has higher memory requirements than previous versions - about 712 Mb for 12.10 64 bit with Firefox, Transmission and a terminal window running. Gkrellm can keep tabs on memory and cache for you as well, or type 'free' on the command line.