Sadly, neither Netkas nor the Russian site are particularly proficient in Engish, so it's not all entirely clear what's going on here, but I'm taking them - Netkas especially - on their word when they say they have found evidence that Rebel EFI is based on open source boot-132 code. Apparently, the Darwin Universal Bootloader, the tool Psystar uses, contains the same strings as boot-132 and tools based on boot-132 (e.g. Chameleon).
That of course wouldn't be a problem in and of itself, if it weren't for the fact that boot-132 is licensed under the Apple Public Source License, version 2. This is a license which contains a clause similar to the GPL in that when you ship modifications, you also have to provide the source code to anyone you shipped your product to. So far, Psystar has not done so, but it could theoretically be that if you ask them, they might provide it.
Now, I place a certain amount of trust in Netkas' words, but his evidence isn't necessarily conclusive. More investigations into the matter will have to be performed to get more conclusive evidence. The Russian site has more information, but sadly, even though I know the Cyrillic alphabet, I don't know any Russian other than Правда and Перестройка, and I know enough about translation to not place any form of trust in automated translations (hint to Russian OSNews readers).
Assuming Netkas is right, this is of course a very bad thing. EULAs can fall off a cliff for all I care, but an open source license which covers distribution is a completely different thing, as any open source advocate and anyone with common sense will tell you. Breaking them constitutes a breach of copyright, which is a serious offence.
I'm not about ready to crucify Psystar just yet - first, let's await their response to this matter, as they might theoretically provide the source code upon request. Second, we do need more evidence (or someone needs to properly translate the Russian page). In any case, it doesn't look good.
On a side note, I just got home from the Apple retailer, where I bought me a copy of Snow Leopard. In the coming days I will test out
Psystar's whoever-owns-it Rebel EFI, and see if it's any good.