I remember fondly learning from tutorials how to make "glossy" buttons. The trick was to have gradients running against each other, with a sharp line in the middle. Now that I think about it, this aesthetic started already with MacOS X and Aqua. Everybody wanted to have the "liquid" style. MS only adopted it with Vista - XP's Luna was famously matte plastic "fisher price" style.
Yep! An easy way is a color gradient background layer and then another layer like a white gradient intersecting it. The orientation/opacity of that top gradient lets you get anything from super-glossy to more of a frosted glass, especially when combined with some additional tweaks to give it more depth.
I still have some websites live (and untouched) from the period if you want to see some...evocative but rather unrefined examples: http://www.biotechgaming.com/software.php (left nav buttons, for example)
Homepage is offline because it has code expecting PHP5 (and Flash); deeper pages mostly work though!
Microsoft adopted it far quicker, but in marginal products. Windows Media center edition was glossy by it's second release, windows media player 9 was glossy (and the aesthetic only progressed further with wmp10), and they released the royale theme which was also glossy
