I have just noticed the same thing!
I have a JPG image sequence from my Nikon. These are 4288 x 2848 Adobe RGB Photo-JPEGs.
In SL 10.6.2, if I open it as an image sequence in QT Pro 7, I get black for all the frames, although the frame counter indicates that all the frames are there. I've tested this on two different machines running 10.6.2.
If I open the sequence in QT on 10.5.8 (on my iMac!), it works fine. If I create a QT movie from the sequence on the 10.5.8 machine, I can bring that movie into After Effects or FCP on SL 10.6.2, and it works on 10.6.2 within those programs. I can see a thumbnail of the frame in the finder, but quickview, get info preview and open within either QT7 or QT10 show black frames...
Here's a couple of possible reasons, although I haven't tested them:
1) Adobe RGB vs. sRGB
2) Raster size of 4288 x 2848 is huge for video, but common for frame sequences.
3) Apple BROKE QT in 10.6
4) Video Card (Radeon X1900 on both SL machines) is misbehaving
Any thoughts anyone? This really mucks up workflow, as you can imagine. Good thing I left the iMac with 10.5.8...
I agree: Apple: HELP!