Hi, does it make sense at all to use Adobe Premiere Pro CS3 on an iMac? Logical to just run it on a PC?

Hello, well, if you're just running CS3, you might as well use your PC. However, Macs are more friendly with this kind of stuff (e.g. Photo Editing, Web Design, Decrypting,Coding, Video Editing and basically all media). Also if you want to do video editing, I highly recommend Final Cut Studio 2. However it only runs on Macs.