I do a fair amount of Rails, so I'm really curious here. How could it be that they've so heavily patched 2.0 that they can't move on? Anyone from Twitter care to comment?

I've worked on many Rails apps, and have upgraded the apps from version to version. It's a pain when key elements of the API shift, but it's not that bad...even when the project has monkey-patched Rails a lot. And twitter certainly has the resources to afford to dedicate a few programmers to this task, so I'm just not sure I buy it.