Just got EQu and it's pretty good, a few annoyances like it not killing the music when I pull out my headphones but otherwise good.
That said, I'm not sure how much I'm going to be using it because the UI is a bit clunky but I do like how I can make subtle adjustments to suit whatever headphones I'm using, it certainly beefs up my HD25s a bit just through the standard headphone out and I'm looking forward to trying it out with my UM SE530x4 reshells which should be arriving later this week. Also going to give it a go with my E6 on the way home from work tonight and see how that sounds.