No, you're not crazy. I used azureus for a long time, and found that it hogged my cpu. Actually, that's why I turned to utorrent, but I think that is pretty heavy on my cpu as well. I like utorrent because it's not java like azureus and clicking around things is faster and it feels more lightweight. However, azureus is more feature-rich, although I don't think I use any of the fancy features.
But back on topic, I don't know if it's the nature of torrents or what, but these programs do seem to use a lot of cpu. Maybe there are other alternatives, like ABC, which I used a little bit, but it seemed to download slower than azureus and utorrent. On the positive side, azureus downloads the fastest of them all I think, with utorrent almost there also.
Maybe because the download speeds are approachin 200-300 kBps is what is making the computer slow. Does anyone know anything about that? I've heard that when you download anything at really high speeds, the computer can become significantly slower. Is that true?