And If we use Python for both, web and desktop/server parts? We will have big problems to integrate these?
I think not.

I like Java, but when we are willing to leave out some maintainability to reach more development speed and similar or better performance, Python is the way to go.

Regarding the speed of Java, I understand that web server software runs continuously without restarting. Most of the Java classes would be compiled by the JIT compiler to native machine code and remain so. Just as fast as C, not interpreted
So servers is where Java really shines and with ease of maintenance PLUS plateform independence and ONE code base.

I’m writing music desktop software in Java using Eclipse. It has a snappy and beautiful score notation interface using Java 2D. For music playback, I get enough timer resolution under Java 1.4.2 to reach an older installed base. Under 1.5, there’s even higher resolution available and updated threading classes.

My application runs flawlessly on Windows and on my old 867 Mhz Mac with no tweaking required so far. I have not tested Linux yet.

It can play 32th notes on my old machine!

Every API and language has its intricacies. With Java, you must learn Design Patterns to appreciate much of the Java API, like Swing for example. OOP Design Patterns make my coding much cleaner - it would in any OOP language. Now I pickup new parts of the Java API quickly. It is quite elegant in comparison to other APIs.

My application IS restarted continuously and it is fast even if byte codes are interpreted.

Making multiplatform applications in Java is as easy as it can be.

For anything big involving web AND desktop applications connected together, Java is the way to go, otherwise you’d have to write parts in PHP/Python (for web parts) and C++/Python (for fast desktop/server parts), but having to integrate these two into one working thing would be so painful that it would blow your budget to the sky. As I wrote, Python could be used for this too, but corporations usually do not choose it because it’s API is changing way too fast and Java is better at performance + offers more advanced features anyway.