I noticed today that a new version of the Phoenix viewer has been released, until recently Phoenix was my viewer of choice but because of impending changes by Linden Labs which will render the performance of V1 viewers such as Phoenix less than acceptable, I personally changed in preparation for the next chapter in SL graphics.
I thought rather than try and explain what this change entails, I would leave it too the Project Manager of the Phoenix team who says it best here as part of her August 2 introduction to the latest version. There are also links to a number of pages that show you how the older viewers will not be able to display MESH objects correctly.
Hopefully her introduction will help clear up any misconceptions you have or at the very least, alert you to the impending changes. The latest version of the Linden Lab viewer will be able to cope with MESH objects but for those who choose to use 3rd party viewers (as I do for increased functionality and improved interface etc) we will need to ensure our choice moving forward is MESH capable.