My Sony Clie PDA has a remote control program built in, and I used Omniremote for my old Palm m505 PDA. The IR ports had a long range, and that came in great help whenever I couldn’t find the remote for the TV or VCR or was too lazy to look for it.
I’d doubt that a similar program would exist for a PC, but I wouldn’t be surprised. But can you imagine picking up your laptop and aiming it at whatever you’re trying to control? What a big pain in the butt. A PDA is fine for that purpose as it’s hand held, but I wouldn’t want to use a laptop as a remote. Unless you’re into working out your arms.