Err, what do you think decompilers are for then?

Well in reversing applications, most people use disassemblers and debuggers to step/trace/analyse the machine code.

Just because they exist doesn't mean what they provide is of any practical value, as you said it yourself they decompile badly.

The Hex-Rays decompiler is very good, and I've used it for reversing several times. In particular, it was extremely useful for our analysis of the Green Dam censorware system (http://www.cse.umich.edu/~jhalderm/pub/gd/).

Thanks for exposing that shipwreck of government-mandated Horrorware.

From the Wikipedia article: "As of 30 June 2009, the mandatory pre-installation of the Green Dam software on new computers has been delayed to an undetermined date."

Source: http://en.wikipedia.org/wiki/Green_Dam

The decompilation quality really depends on how obfuscated the original code was, and how much time you care to invest. For example, I'm using Hex-Rays to decompile Command & Conquer: Red Alert 2 and extend it, and now its output looks like [1] , which is a lot better than raw assembly menemonics. Though I've been digging into this game since late 2008, which is a long time.

[1] http://img824.imageshack.us/img824/1188/hexrayscpp.png