If you write web apps that fit comfortably in
one or two boxes you'll likely never need the speed.
This is hand-waving the fact that the JVM really is good only for server-side applications, and nothing more; mostly because bindings to native APIs are shunned by Java developers and because Java SE may be fast, but it starts slow and it consumes tons of RAM -- 16 years after Java was launched, 16 years of Moore's law, and Java apps still feel like crap.
It is kind of ironic that if you want to write well-behaved OS X, Gnome, KDE or Windows apps without dealing with Obj-C or C/C++, you're better off building on top of Ruby/MacRuby, Python or Mono/C#.
It is kind of ironic that if you want to write well-behaved OS X, Gnome, KDE or Windows apps without dealing with Obj-C or C/C++, you're better off building on top of Ruby/MacRuby, Python or Mono/C#.