We've just put Praxis Works rings onto our entire rental fleet for this season - a nice upgrade for our customers (http://lafugatravel.wordpress.com/2012/ ... tal-bikes/
). Most were being swapped in as replacements for the stock 52/36 sets, but on the few bikes that already had other 50/34 rings installed, there was no need to retune the front shifting.
I suppose in theory, some ring sets might have a different off-set from their attachments to the cranks, but in practice, I found the alignment was the same for either the SRAM or Shimano rings that we replaced - these were on SRAM and FSA cranks.
Oh - for what it's worth, the rings are killer!