I posted this on the C3D forums, but maybe it can be helpful to have it here too, as not everyone goes to C3D for forum duty anyway :)

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People who prefer to deal with the user settings directly (like me) won't be affected, but people who use broadcast, superior and mostly ultra presets will be (the preview and final presets haven't changed).

Following a discussion with e-on developers, and after seeing people using the Ultra mode on the RANCH without really knowing a lot about the implications of the old 'Ultra' mode (that is, in some cases it could lead to the scene taking more than 30 - yes, thirty - times longer than in Superior mode ), the Ultra mode has been toned down in post-290396 builds.

Here is a quick comparison between build 290396 and build 291050:
OAA=Object AntiAliasing
TAA=Texture AntiAliasing

• Broadcast
  290396 - OAA: 4-16 (60%) TAA 4-12 (80%)
  291050 - OAA: 4-16 (60%) TAA 4-12 (60%)

• Superior
  290396 - OAA: 4-24 (70%) TAA 4-24 (90%)
  291050 - OAA: 4-24 (70%) TAA 4-16 (70%)

• Ultra
  290396 - OAA: 4-32 (85%) TAA 4-28 (95%)
  291050 - OAA: 4-28 (80%) TAA 4-20 (80%)

And most of all the 'Recompute Subrays' option is now unchecked by default in Ultra mode.

All this means that in scenes with heavy reflections/refractions, builds > 290396 will be considerably faster in Ultra mode, and slightly faster in Superior mode (for broadcast it won't really be noticeable). The difference in image quality will be very small for most scenes, compared to the massive speed gain. There may be some cases - for example scenes with blurred reflections - where you might want to reactivate the 'Recompute subrays' option to have extra quality, but of course with astronomical render times.

All in all the new settings are more balanced. New Vue users have a tendancy to throw the ultra mode at everything, and it was painful to explain that even on the RANCH, you could cook up some scenes that could take days to render Now it shouldn't happen, except if someone messes up with the user settings without knowing exactly what parameters does what...