Ooh, sweet avatar.
Well, my two Maxtor 40GB IDE's barely put out any heat so I haven't experimented very much.
But according to WD those 200s are rated up to about 55c operating temperature, which is darn hot for a hard drive. I'd say mid-30's would be a respectable goal, but those puppies could put out a lot of heat for all I know. There's also a feature built into many hard drives called Self-Monitoring Analysis and Reporting Technology (S.M.A.R.T.), which can report on stuff like temperature and drive health. Again, I haven't experiemented with that much but it could be an easy way to monitor your disks.
BTW, you have a TON of nice drives! Almost give Mantra a run for his money.
(Although I think he tops 1TB hehe)..