What about the new 2012 process in regards to the older processing of Lightroom 3.0 - 3.6
do these remain the same or will every image be converted into the new 2012 processing
algorithm upon conversion to Lightroom 4.0
When you convert your catalog from LR3 to LR4, all of the images in the new LR4 catalog remain in the old process (called "Process 2010") unless you specifically change the photos to the new process ("Process 2012")
One by one, go to Develop Module and click on the exclamation point that appears at the bottom right of the photo
In bulk, change one photo to Process 2012 (as explained above) and then using the filmstrip select multiple additional photos (Ctrl-Click or Shift-Click) and hit Synchronize, then click on "Select None", then check Process Version and click OK.
You might not want to do this in bulk, as the appearance of your photos usually changes when you convert to Process 2012. If you do it one by one, you can make sure that the appearance is what you want, or adjust it if it needs further adjustment.