It's really hard to build trust when products disappear. Building on top of google is hard for this reason, and Facebook is beginning to look eerily similar. Recall all of the wonderful social graph access that once existed and see, now, the wake of crippled API's where they once lived.
Since it is impossible to build everything from scratch, some compromise must be made, but I wonder whether that compromise can reasonably include offerings from $BIG_CO? Certainly open-source projects implode as well, but rarely with the scale of things like Google Reader or Parse...