There is a post up on the Second Life™ BLog: Fitted Mesh Is Here!
What this means is the avatar and viewer have been finalized for the Fitted Mesh Project. The Release Candidate Viewer has rolled out and is now the main SL Viewer.
Within a couple of days the majority of those using the SL Viewer will be running the new viewer and capable of seeing Fitted Mesh clothes correctly.
I suspect Jessica was hinting that the Firestorm viewer with Fitted Mesh is going to main release version. Other third party viewers support Fitted too. So, very quickly the majority of SL will be able to see Fitted Mesh clothes rendering correctly. I am certain 60% of SL users will be able to see Fitted Mesh. I am pretty sure the number is going to be between 80-90%. But, I have only my opinion to base that on.
Advanced Lighting (ALM) is not important to whether you can see Fitted Mesh. Enabled or Disabled the Fitted Mesh will have the same shape. ALM may affect how the material used on the clothes looks. If the designed used the new Materials feature to make the clothes they will look different depending on whether ALM is enabled or disabled.