Basically, LJ's code has always had one gatekeeper -- Brad. He says what goes into the code or not, and he says what will be open sourced and what won't. Now, there's *already* some evidence out there that LJ is willing to hurt those LJ code sites that compete most effectively with them, but yet there *IS* no talk of LJ designing its software to have better interconnection / closer ties with other LJ code sites... only with SixApart weblogs.
Currently, changing to other services is a pain. The difficulty of moving your site to another LJ-code site is prohibitive, LJ is already withholding source code to make those sites less competitive, and the kind of interconnection that may make it easy, for instance, for you to have an account at DeadJournal or GreatestJournal or... and add LJers or LJ communities to your friends list not only doesn't exist -- it probably won't exist, because SixApart has no motivation for improving the LiveJournal's GPLed codebase.
The only way out of this trap is to make LJ's code seperate from SixApart and to take away Brad's veto power over what goes into the software... but the people who know the code best are also the people most likely for SixApart to hire. And of course, SixApart can be bought out by any company with enough money once they go public, so LJ's future is far from secure, and Brad's former "contract" which has now become "guiding principles" may mean nothing a year down the road.
In other words, the rules have been changed on us -- even if we paid in advance -- and we're all locked in. Enjoy the ride.