I was going to buy Zend guard this week, but one of my friends told me about Dezend. At the beginning I didn't believed him, but he sent me the program, and told me I can test it myself.
I've tried zend guard trial with all obfuscating (max) options, and made my encrypted php. then tried Dezend, and surprisingly, it decoded all my data, without any problem.
I strongly suggest Zend, to include the compiled state of code into encoded php, as any encryption that should be decrypted, and be used in php framework. but when you store only compiled stage of your code, its impossible to restore your code, and at the best condition, it can be *ONLY* disassemble, that is useless in almost all ways.
I'm really looking forward to here official zend response about this...