For me, a handful of designers come to mind when thinking about exploring new modes of male dress, modes that had previously been considered 'female': Riccardo Tisci for Givenchy, Rick Owens, and Gareth Pugh.
Let's take a look at Givenchy. For the upcoming FallWinter2010 collection, Monsieur Tisci sent out an array of masculine skirts. All were to the knee, some were in heavier wools, others in velvet. All were flattering and refreshing. Givenchy has also been into leggings lately. Male leggings were all of the Spring 2010 collection and have carried into the Fall 2010 collection. I think what makes his entire male-shirt-and-leggings discourse so interesting was the use of Christian iconography and costume. The models were styled with Crown of Thorn necklace, one even sporting a TShirt which read "JESUS IS LORD." What does it mean to invoke Christian ideals of the Christ figure when experimenting with male skirts, male leggings? Are we supposed to remember that the Lord himself, by far the most influential person in history, wore glorified dresses?
ANYWAYS I digress. My point is here, ladies and gents, that male leggings and male skirts are coming in and there is nothing you can do about it! With the likes of fashion icons (?)(figureheads?) such as Andrew Mukamal being brought to forefront of pop culture- for those of you living under a rock, I am referring to Bravo's 'Kell on Earth'- and couture-tier houses producing ready-to-wear gender benders, it's only a matter of time until male skirts and leggings go mainstream. Here's a great street style pic of leggings done RIGHT. Although I am still not sure about 3/4 length versus full-length leggings. I think it depends on the shape of your leg. But whatever.
And this kind man had the decency to wear the leggings under shorts, so you prudes have no reason to pull out your "but we are so afraid of the visible bulge!" crap.
I think you get the idea. Here's some more men in skirts and leggings for your consideration.
But as of now, it seems that the trend is going to remain that leggings will be worn under a constructed bottom instead of hiding under a long drapey top. Even the fashion forward are too afraid to completely let loose the penis.