I honestly can't believe how little attention and love this product gets!! I am a total primer junkie, and this blows the pants off ALL of them, even my former beloved LP Rose Illusion and board fave Clarins Instant Smooth Perfecting Touch.
Other than LP and Clarins, I've also tried Clinique Pore Minimizer, Smashbox (several varieties), MAC Prep + Prime , Revlon, Lumene, Michael Marcus, Laura Gellar, Giorgio Armani (US and 2 Asian versions), BE Prime Time, Lorac, Sue Devitt, and Laura Mercier (mineral and regular). I generally do side-by-sides to check performance. This beats all of those handily.
This smooths out pores, prevents fdn from getting at all clumpy or breaking apart during the day (this happens around my nose sometimes- KWIM?), and somewhat controls oil. I wonder if people are put off by the name "Matt Touch"? It doesn't really make me matte, just smoother and not-oily-shiney.
This is also a fairly well-priced option, definitely cheaper than both LP and Clarins. The packaging is also superior- a simple squeeze tube, instead of the heavy and unsanitary jar many primers come in. I am on my second tube and will continue to buy this!
Update 02/21/08 : I am now on my fourth tube and still loving it. I've never had a problem with the product smelling or balling up like reneeg. I will agree it is thicker than many primers, it is most similar in thickness to Clarins, but not as thick as Michael Marcus. I will also admit that the GA US primer (which is a thick clear gel) and the Chanel primers (I've tried 2, have a third on the way) are also excellent options I have in rotation with my beloved YSL. Like Saloco, I think YSL gives me the best balance of smoothness, slip, and longer-lasting fdn.