Why has my macbook fan been running all day?

you most likely have a process taking up a lot of CPU resources. Open activity monitor, sort by CPU usage and see what’s taking up processor cycles

also make sure your firmware is up-to-date; Apple released a recent EFI firmware updater in their downloads section for MacBook Pro’s

And, er, silly question—is the MacBook sitting on a soft surface, or otherwise occluding its vents? It might just be hot.

Thanks sapridyne.. I checked my processes and one of my widgets for some reason was using up a lot of resources :)

no problem. glad i could help.

I found an old print job still trying to print. I used activity monitor and stopped the print job. Ahhhh silence again.
mike
va