My domains haven't seen an increase, but individual pages have. Clients' sites have gone up too.
I'm going to test poor optimization techniques on throwaway domains and cheap hosting. My sites are increasing in PR, sure, but they're doing it pretty legitimately. Even the SEO, apart from being tiered, does consist of quality, so it's not exactly "blackhat" sites increasing in PR for me, you know?
...One of my sites just got 3000 backlinks indexed from 17 domains, so I guess someone hates one of my sites, cause I didn't do that.
In regards to PR update frequency, I've noticed an almost immediate change when there are indexed backlinks. New content hasn't been increasing PR by itself, but maybe I've just been impatient. I'll try to just add content and no backli...but then I won't get traffic for ages. I'm unsure about what to test.