It definately works, Matt Cutts was caught doing it on his blog a few months back!
He ended a post like this:
There's many kinds of SEO: Longtail SEO, onsite SEO, offsite SEO, Local SEO, video SEO, SEO SEO, Search engine optimisational SEO, SEO for small businesses, SEO for large businesses, SEO for ecommerce sites, etc, etc, etc,etc
You get the idea, the paragraph was freaking HUGE, and it was nothing more than a bunch of long tails separated by commas!
When he was called on it his toady sycophants piped in "Oh thats not keyword stuffing, thats just the way Matt talks" What? Like Rainman?!?!?!
(I would post a link, but I'd need to find it on his site and every time I visit I throw up a little in my mouth)
Far as Im concerned if Matt's done it on his blog it can't be bad, but further more if Matt does it, and denies he did - you know it works!