I had to edit a load of videos for a presentation a few months back. I tried it on the iMac I was using, but iMovie was just getting in the way. In the end, I did it on a Windows 7 machine with Microsoft MovieMaker!
One of my problems was having to take video from various sources (Elgato Game Capture HD (iPad and Android tablet app captures in full HD), Adobe Captivate and our company film on DVD). iMove baulked at the Captivates and didn't much like the Elgato either, even though the Elgato captured onto the Mac!
Switching to the PC, I actually had to re-export the Elgato film on Windows - which in fact then turned out to be something that iMovie could use! Why iMovie couldn't use the Mac version of the video is beyond me, you would have thought that Elgato Mac software would export to a format that the Mac can work with...