i was one of the designers on loopt.com, and the reason i think most of these sites look the same is because we all go through y combinator hearing the same thing: "the number one enemy is the back button." we just don't have time to overload the home pages with too much stuff if we intend on someone doing something while they're on it. so i think all styles gravitate towards a similar highly-focused product-oriented design.<p>as for the actual ui elements. i think a lot of companies out there, specifically the freelance design firms, are taking their inspiration from apple's mac os x ui elements. the gradients and button styles are very similar, and then other freelance designers will look at that and try to find ways to change or improve that even further. i think it all ultimately derives from apple though.<p>many designers i know of will use a css grid framework; we used grid 960. the reasoning behind the number 960 pixels is described on their web site:<p>"All modern monitors support at least 1024 × 768 pixel resolution. 960 is divisible by 2, 3, 4, 5, 6, 8, 10, 12, 15, 16, 20, 24, 30, 32, 40, 48, 60, 64, 80, 96, 120, 160, 192, 240, 320 and 480. This makes it a highly flexible base number to work with."