I've been following NaCl, and it worries me that the compiled code only works on a particular version of Chrome. NaCl 0.5 only works with Chrome 14, 0.4 works with Chrome 13, etc.

http://code.google.com/chrome/nativeclient/docs/running.html#browser

Downtime comes from people. The more people involved, the more downtime you'll have.

Two weakest points of Java are:

1) Date/Time objects
2) Generics

as compared to C#/.Net -- having worked professionally in both. No langauge is going to fix these two.

(Though you can use Joda for date/time handling.)