This may not have relation with Perian, but I guess people may know.
I've used to import DVD videos (MPEG-2 video with AC3 audio, generally) on Premiere Pro with Snow Leopard with no problem, but have no luck on Lion (it displays the message "unsupported compression format"). Lion comes with MPEG-2 support for the Quicktime X player, yet it seems that Premiere relies on the Quicktime 7 codecs, which don't support MPEG-2 on Lion. I did the Squared 5 solution to put the old MPEG2 component back, but the videos still don't import correctly on Premiere. Only the "video" track appears and is a completely black still at 0fps. Only the video "length" is correct. If I import the audio demuxed, says that it don't recognize the format. The video plays fine on MPEG Streamclip, yet the last time I exported a MPEG-2 video from there in another compressed format to use in Premiere, the Premiere output video ended with the colors all wrong. Quicktime 7 plays the videos, but sans audio. It frustrates me a lot especially since I could import the very same videos directly in Premiere without problem with Snow Leopard.