Pdf.js: PDF Reader in JavaScript 
1) From a technical perspective, this is damn cool - exceedingly well done. Color me very impressed.2) I hope I never actually see anyone using this on a website, attempting to make things "easier." Between Scribd and Slideshare, and Adobe trying to force its hideous crash-prone plugins into my browser, there are already enough people making a mess out of what is one of the more well-thought-out aspects of OS X. Give me a link to a PDF, which Preview.app handles in wonderful fashion any day.3) It would make a sweet browser plugin on browser-in-a-box platforms and other platforms that don't have a nice native implementation (which upon further reading seems to be the goal).