If it's crap ... We'll tell you
Yes, Up used 3D excellently! I did leave Avatar with a two-day migraine, however.
I have to admit that back in the good old days the 3-D in Spy Kids 3-D Game Over sucked because Robert Rodriguez used the traditional anaglyph projection instead of using James Cameron's polarized projection only viewable in special venues.
But now 3-D has improved thanks to RealD 3-D. I love seeing animated movies that have effective 3-D. The only live-action movies that should be in effective 3-D are the Avatar trilogy because some live-action movies that I have seen in RealD 3-D have little 3-D unlike animated movies.
I have been purposefully seeking out films in 2d for the last year or so instead of just going to see it in 3d.
I am a 3D fanatic/enthusiast but by now, I am so burnt out seeing every fifth movie coming out in 3D. However, movies like Tangled and How to Train Your Dragon were really special seen in 3D. Conversion 3D movies, however, I totally detest.