A month or so ago I received an email from American Apparel containing a 30% off discount code. The AA disco pants have been circulating fashion blogs for AGES, but I could never really justify the excessive pricetag (£74), so I decided to take advantage of the discount. I got them for about £55 including delivery (still far too expensive for what is essentially a pair of high-waisted leggings, but they were an impulse buy...)
Being a UK size 6/8 and with the website recommendation to go down a size if unsure, I opted for an XS, but was shocked to discover just how tiny they looked when I first opened the package. However, fortunately they are made of an extremely stretchy material (90% Nylon, 10% Elastane) and they actually fit perfectly. They're flatteringly tight, but they don't restrict your movement in any way.
They're interesting in that they're not quite leggings and they're not quite trousers, but they're definitely thick enough to be worn on their own. They're comfortable enough to wear casually during the day, but also look great dressed up for going out.
Overall, i'd say that if you're willing to splurge for the real deal they're a great investment piece. However, many high-street shops have recently started making great cheaper versions, such as these from Topshop which are less than half the price (though arguably not as good quality).