Autodesk Labs got some attention of late, but Adobe also has its labs.adobe.com site. Over there you'll find Digital Editions, a lightweight replacement for Acrobat Reader -- which had been getting fat and slow, especially with version 6.
Digital Editions is based on Flash, but opens PDF files in a flash. Right now, all it does is display pages at a variety of sizes, as well as do searches of the document. Naturally, it'll display CAD drawings converted to 2D PDF, but from the FAQ it appears 3D models will never be supported.
Adobe calls the software a "rich Internet application," which means (1) it can be installed only from the Internet; (2) it checks for updates each time it is run; and (3) it'll be displaying advertising to pay for itself. When I tried it out on one of my e-books, it worked as promised: loads fast and displays PDFs.