The very most right-leaning web framework is PHP: it's so right-leaning it's not really a framework. Pylons is very much a "right-leaning" frameworks (someone at PyCon referred to it as a "drawing of a hammer" in contrast with the famed hammer factory factory featured in a Joel on Software blog comment ). Zope is very much a "left-leaning" framework (it is certainly the most left-leaning Python framework; I suspect Smalltalk frameworks would be left-leaning but I've never used one so I don't know). Django and TurboGears fall somewhere in between, though maybe they're more right-leaning than left leaning. I suspect Apple's various frameworks are pretty left-leaning, but I'm not really an Apple developer either. UNIX is a right-leaning framework; Windows leans more left.
"Right leaning" frameworks place more responsibility on developers, end users and integrators. Therefore, they are usually materially simpler than left-leaning frameworks, which tend to assume a lot of the responsibility that isn't provided by the right-leaning variety. On the other hand, left leaning frameworks, because they provide a lot of functionality are typically harder to understand and develop for initially, because you need to understand a lot more before you begin to write code but they tend to provide features that can prove useful later in development and deployment that are ignored by right-leaning ones.
This distinction has consequences on applications developed within them. In applications developed in "right-leaning" frameworks:
In applications developed in "left-leaning" frameworks:
It's often far, far easier for people to start writing code using a right-leaning framework than a left-leaning one simply because there's a lot less to learn. A poorly-documented right-leaning framework is easier to develop in than even the best-documented left-leaning framework. If you're just starting out and you need to develop an in-house application that won't be redistributed or reused, a right-leaning framework is almost certainly a better choice: many of the features of left-leaning frameworks are there to support redistribution and reuse.
On the other hand, if the goals of a left-leaning framework line up with your problem domain, despite a steep learning curve at the beginning, it might be wise to use one rather than a right-leaning framework. For example, Zope is exceedingly good at providing arbitrary-depth document hierarchies out of the box, whereas this behavior tends to need to be created from scratch for each job in right-leaning frameworks. It's typically far easier to retrofit a Zope application to go "one level deeper" than it is to retrofit an application written in a right-leaning framework.
All that said, personally, I'd like to see Zope lean a little more right. Because it has so much history, it's pretty difficult to make it do so. Our shot at it has been in the form of Repoze which attempts to make Zope do less by pulling functionality out of Zope and into smaller distinct pieces. These pieces should be more easily understood and used by people who don't want to bite off an entire left-leaning framework. They can even be used by people who might otherwise be using right-leaning frameworks. Grok leans more right than does Zope, which is gret, but it's still more left-leaning than any of the other existing Python web frameworks because it has historically had a focus on general "approachability". This drives its inventors to want to solve very general problems by writing more framework software rather than by placing particular bits of responsibility on end users.
I imagine a lot of the current right-leaning frameworks will evolve more left-leaning tendencies as they become more ambitious. Both Django and TurboGears seem to be shaping up this way. This path needs to be treaded carefully, but I think both of these communities have excellent leadership, which should take some of the risk out of "going left". In the meantime we'll go at it from the other side, trying to pull bits out of Zope that should form a slightly more right-leaning set of components. The future looks very bright. Viva la 4th generation of Python web frameworks!