I'm running this on a MacbookPro6,1 with a 2.66GHz Core i7 and 8GB of ram on Mac OS Lion (10.7.1). I have an nvidia geforce gt 330M with 512MB of vram.
I have a 500GB SATA HDD. Mac OS is on a 300GB partition and I have ~30GB of free space.
I'm running Premiere Elements 10.0 (20110902.B343.280460) Trial.
My project has 9 AVCHD files imported from my camera (MTS). They were shot at 1920x1080 at 29.97 fps with square pixes at about 2MB/s. In all, the clips total just over 7 minutes.
1. Sometimes when I drag a clip into the timeline or drag the yellow lines in the timeline around, the clip boxes don't stay anchored where they're supposed to. They jump down about half a box height and change color. It's very hard to tell what's going on when this happens. Note: I've only experienced this on the first run after install. Since reloading my project after restarting pre10 I can't get this to reproduce.
2. Horizontal scrolling in the timeline is slow. At times it's so slow that the timeline gets confused and jumps back to where I started scrolling from. This happens with both 2 finger scrolling on my touchpad (totally unusable in this app) and with the scrollbar (slow but passable).
I've been impressed with what I can do but I'm wary about purchasing on Mac OS with these issues.
When you started your project, did you ensure that it was set up for AVCHD 1920x1080 to match your camcorder video?
The AVCHD component for the program is one that needs to be activated, so it's important that you set up your project correctly in order to turn on support for this type of video.
Also, did you use Premiere Elements' Video Importer (under Get Media/From Flip, AVCHD and Hard Disk Camcorder) to get the video from the camcorder to your computer?
It is possible that the free trial of the program doesn't support AVCHD. I don't know that for sure, but it is a possibility. Contact Adobe and they should tell you.
But I'm running version 10 on OSX Lion -- on a dual core iMac! -- and it handles AVCHD almost as well as it handles standard def DV!
Trials do support AVCHD. Only difference between licensed and trial in case of PRE is that trial will show watermarks at every place. Please make sure you are working with correct project settings and if horizontal scrolling is slow, please turn off large thumbnails view of frames and use the default one.