From personal experience decompiling Java, I will say that obfuscation can make someone's attempts to decompile very very irritating and difficult. The most irritating to me is when the final builds class files are all named "a.class, b.class, c.class" and so on, and a large amount of dummies are thrown in. In terms of in code obfuscation, try/catches do a fine job of messing stuff up for the decompiler.
In general, anything you decompile will not be compilable, but will give you hints as to the general workings of the program.
