 When to release? 
rg: One thing to consider is to what extent the user will be depending upon the quality and comprehensiveness of your specific product.  A product used for recreation or convenience may be very partial and/or may fail frequently without causing much disappointment, and users may be happy to have it early.  In contrast, my startup made a product that many users considered vital to their professional and business success, that required substantial initial investment of effort, and that users often used under considerable time pressure.  Anyone starting to use the product who became  wedged by incomplete features would be extremely unhappy.  For this product, it was necessary to get it over a fairly high threshold before offering it (apart from a demo or alpha with no expectation that it could be depended upon).  Most products aren't in this category, and profit from early release.  But even so, for your specific example, I tried Pandora on its release day and was disappointed, and wrote to Tim Westergren to tell him so; he answered within minutes promising future improvements, which should have been impressive enough, but it took me two or three years before I tried Pandora again (I'm now an enthusiastic paying subscriber).