Update (22 June 2008): I've posted a Python script for converting the invalid permalinks to their "proper" form.
After moving to GoDaddy I found to my chagrin that none of the site's article links (a.k.a permalinks) seem to work. There are any number of reasons why this is a bad thing, the two primary reasons being that Google cannot crawl the actual articles and that historical, incoming links no longer work. As they say, crap on a stick.
I originally looked into the URL rewriting rules and HTTP handler configuration in web.config, thinking that perhaps some of the handlers need to be manually registered with IIS for some reason; eventually I installed the blog locally, migrated to IIS pipeline mode (which might be cool but has no tangible benefit for me) but the problems persisted. Until I tried accessing a permalink URL locally, that is. Then I discovered that plus signs in URLs (dasBlog's way of avoiding encoding spaces to %20) are considered "double-encoded" characters, and are automatically rejected by IIS 7.0 by default because under some circumstances they pose a security threat.
There's a knowledge-base article detailing how to resolve this on a server or per-application level, but either solution requires server reconfiguration. Working under the assumption that this entails special requests from each and every potential future web host, and that having plus signs in my URLs is not the "right thing to do" anyway, I just opted to disable them and try to rework the existing links as best I can. I suppose blogs with considerably higher traffic cannot afford that luxury, but then blogs with considerably higher traffic usually work with much more specialized hosting providers and wouldn't have to worry about server reconfiguration in the first place...
Anyway, hope this helps someone.