I'm running late 2013 13" rMBP 2,4/8/256 and I'm experiencing quite large performance issues. Let's start from the beginning. I've downloaded trial version of FCP X and used it recently for a small project. The software is amazing and worked really well. Unfortunately I have more pressing expanses right now rather than 270 software. There's another project that I decided to do in iMovie 10 as FCP X is due to expire this week. This project is much longer - the video is 2 hours and 20 minutes long. THE ISSUE: The video is imported and ready to go. I know that because external HDD's LED is still so it's not working anymore. If I try scrolling the timeline I get a slideshow with framrate below 1 per second. Dragging parts of clips to the timeline is even worse (wow, that's really possible). I've discovered that if I zoom out (so long clips are short on the timeline) the program is starting to work a bit more fluent. And yes, I don't have to drag clips to timeline - there's shortcut for that. Here's the funny part - I tried doing the same thing with FCP X as the trial has not yet expired. It works brilliantly. Not even a frame dropped. I thought that maybe iMovie has issues running in HiRes, so I've forced it to run in LowRes - it's the same. Here's my conclusion - I know that Apple has to somehow encourage people to buy FCP X. I just wish it wasn't performance of timeline scrolling. Or is it just me? EDIT: Could it be that unlike FCP X, iMovie has issues working with library/files residing on external HDD (USB 3.0)?