Yeah, I've been trying to find out myself. All I get is the vague fob off response from tech support (Jose). Standard/limited-version is "without added effects", but he won't list what these effects are (saying they're "classified")! Is it ALL the effects that aren't available? Or just the two watermark effects (image/text)?
I installed an update and didn't register it yet (coz I don't know which one to upgrade to). These are the effects that seem to be currently available (in the unregistered version)
auto color/contrast
brick
brightness
border
cartoon
contrast
crop
filter - b&w / sepia / negative / levels
flip
resize
rotate
saturation
vigenette
watermark image/text
So it seems that it might be better NOT to register because then you lose access to some or all of the above effects... :o