Skype is constantly eating 10 to 15% of the CPU on my MacBook, and makes it hot even when I'm doing nothing. Is it because I have close to 200 contacts and usually more than 15 open chats?
I have about the same number of contacts on Adium, and it usually stays in the 0.5 to 1.0% CPU range.
There should be an environmental ranking for software, according to the amount of CPU they use while just waiting...