By export do you mean that runnable package generated when hitting <CTRL> + E?
I'm in Linux using 64-bit JDK 7 for both Processing 2.0 & 1.5.1 and haven't noticed any performance diff.

Of course, since P2D, P3D and OPENGL don't mean the same for both;
some types of programs would fare better or worse than others while running in P2+ or P1.5.1.

If you're are talking about the export to web feature, then yes, this is a problem that you will experience from time to time.  Javascript is not as fast a language as Java.  Additionally, browsers are not as fast as native applications on your computer.  JS is much less forgiving than Java for inefficient code.  Often refactoring helps. 

I'm not talking about export to web, I'm talking about export to standalone app.

Bigger overhead, I guess... just my 2 pence...

Do you have any data to backup your statement?

My various codes use Java2D only, don't use additional libraries, and in general consist of combinatorial optimization algorithms on graphs.

And what amount is the slowdown you measured? A few percents? An order of magnitude?

My intuition was telling me that there may be differences in imlementation of the default 2d renderer across processing versions. I did a simple test and it suggested that 2d drawing in P2.0.1 is about 4.5 times slower than in 1.5.1.