The big question at the moment is how will Apple take this? Apple filed a complaint with the US Copyright Office last month claiming that jailbreaking is illegal. They're not going to take firing a direct salvo at the App Store itself lightly. There is competition for the iTunes Music Store, but Apple could argue that the homegrown app stores infringe on its copyright by using modified versions of its software.
It's not a huge shock that App Store competition is popping up; the only surprise is that it took this long to happen. After all, developers are frustrated that excellent programs such as Podcaster are passed up in favor of the latest, greatest novelty app -- then to make matters worse, those same features turned up in an official iPhone update.
While there are a lot of really terrible apps out there that have no place on the App Store -- I won't even begin to tell you about one adult app pitched to TUAW, we do want to remain a mostly family-friendly site -- there are a lot of good software that get turned down because of Apple's stringent developer's agreement. These developers want an avenue to distribute their programs, and homegrown app stores are one answer.
Cydia's Jay Freeman told the WSJ that he has lined up a lawyer in case Apple comes knocking at the door. He may also want to get in touch with the team that represents Psystar ... just in case.