I've been running current (just built the world with a sup from early
   morning May 3rd) with UVM.
   
   I have a sparc10s with 32Mb of RAM.  I believe the machine has been
   more stable, but I have no hard data.  I have not noticed any change
   in performance, but it doesn't have enough memory; so it pages all the
   time anyway...


paging performance should be greatly increased under UVM -- the pageout
operation was between 4-8 times as far under "heavy load" than the mach
VM was, which gave me a much more responsive system (this is mostly due
to the clustered pageout chuck and i implemented).