Superb earphones if you can get the right fit,
This review is from: Ultimate Ears 300vi Noise-Isolating Headset (Electronics)
I've had these for a few weeks now and use them solely for the gym. It comes with a nice selection of ear buds to suit your size and this is key. If you can get these to fit properly in the "sweet spot" they sound amazing. The bass is superb.
My biggest issue has been finding the right combination of ear buds that fit my ears. These earphones seems to be very directional, in that if you havent got them positioned in exactly the right place you either lose bass from the lack of seal with the buds around your ears or the sound gets totally blocked and you can't hear anything. I find that what I start with before a workout and what sounds great seems to change once I've moved about a bit and got sweaty. I'm forever adjusting them to get them to sit in that sweet spot and after each work out Im trying out different combinations of earbuds until I find the perfect mix. My ears don't seem to be symmetrical so I'm even looking at using different sizes for each ear.
The loop around the ear fitting works fine for me, I've not found them falling out completely but you do get a minimal amount of movement as mentioned above.
A final note for android users, I use these with a HTC sensation currently on gingerbread 2.3.4 and although they work as a handsfree set only the middle button works. I've got round this by using a free app in the market that allows you to use a combination of single button presses to skip tracks, fast forward/rewind adjust volume etc... I thought this would annoy me but its actually not too bad a work around.
So to conclude, an amazing sounding earphone so long as you can get the fit that works for you. So based on this and the android button issue its 4 stars.
****EDIT JAN 2012****
The right speaker gave up similar to how others have reported. Had to send it back for a refund as no stock left.