Whether it's still relevant or not CUDA has a lot of mindshare in the academic community. Partially this is due to marketing and having their product out first, but also OpenCL has to go through some more abstractions. There was a quite popular forum post[1] a while ago now where someone claimed a 5x perf improvement from switching from OpenCL to CUDA and, while i havn't tested it myself, it's the sort of statistic that sticks in your mind.

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1. http://forums.nvidia.com/index.php?showtopic=109684