Hi
(Later)
Further to the above posting which was a test with a single clip project...I have just tried to load another more complex 2.41 project into VP 3.1
It's a short film of 11 mins 20 seconds duration.
OK.....it loaded (APPARENTLY) and so far has not crashed.......BUT.... I say "So far" as it is STILL generating things after 40 mins!!!
The project consisted of 57 short video clips, 2 or 3 being stabilized avi clips. They were all 1280 x 720 MPG4. clips The project included 4 snapshot images and three audio files and the editing included numerous audio clips for narration and crossfade transitions between a proportion of clips.
Starting with a completely empty cache file, the project loaded the clips to the media list in 2 mins and then took 2 mins 30 to generate the thumbnails for them in the list.
However it proved impossible to preview the film (and do further editing) as the green bar was so slow to move along the sequence and all that came up was the "Building Preview" screen. (I think this has been made to regularly invert)
Even when the red cursor line was moved to a "green barred" section it refused to preview.
AFTER 30 MINS THE GREEN BAR WAS STILL MOVING ALONG THE SEQUENCE LINE GENERATING THE THUMBNAILS THERE, BUT HAD ONLY REACHED THE 6 MIN MARK. TRANSITIONS WERE STILL ALSO BLANK.
IT TOOK 45 MINS TO COMPLETELY LOAD ( APPARENTLY), WITH SEQUENCE LINE THUMBNAILS ETC.
THIS WOULD NOT PREVIEW AT ALL BUT PLAYED THE SOUND TRACKS ALL OUT OF SEQUENCE.
**ALL TOGETHER THIS WAS A TOTAL FAILURE! 
Following this test my advice is NOT to load any 2.41 projects into VP 3.10.
I have not created any large projects with 3.1 (or 3.0x) versions as I still mostly prefer 2.41 so I don't know how a big project would load from scratch.
NOTE:
As a comparison... The same project used above loaded into V2.41 from an empty cache and was ready to edit in 2 mins 25.
When loaded with the cache present it took 15 seconds!
Nat