I have barely used the Pro 3's, but have more miles on the Pro 2's than all other tires combined, and they consistently performed very well. I never had any cracks.

I have a pro3 on a rim that was installed before Texas time trials in 2008. Other than a lap or two out there, it wasn't used.    It's been hung in a garage for the entire time.  No cracking.      That being said, the pro3 is exceptionally thin everywhere it's not critical to save weight.  It usually only takes a mis-seating of a tire (where tube blows it off) to ruin one with my carbon rims.      The rubber on the sidewall really doesn't provide any structure to the tire, I'm not sure I'd fret too much.      
 
That being said, I really preferred the pro2 tires for commuting/beating around.  For a 'fast' tire, the pro3 is hard to beat.   I still have some 25mm pro2's on my Fuji and they are going strong.   Usually got about 4k miles out of them on the DF in racing type conditions.  I'm lucky to get 2k miles out of the pro3's in similar conditions.   Not because I wear them out, but they pick up enough nicks that I won't go into a race with them not being minty.  
 
If you need 700c pro3 tires, drop me a note.  I have red/orange/back in stock currently.   I buy around 100-150 units at a time for my ebay biz.  
 
 

Yup.  But I can do better locally/cash on tires.