Works as advertised, though it definitely would be much more useful if it filtered the content through Readability (or similar) before pushing it to the Kindle; without such a filter you run the risk of having to sift through all kinds non-content stuff, which can be terribly annoying on a page-at-a-time e-ink device.
Accordingly, if the site doesn't offer a print-friendly formatting option (read: most sites, especially blogs), you're kind of out of luck and probably are better off reading the article on your computer.
If you, like me, find yourself not using RekindleIT as much as you would like because of this very issue, then I've some good news for you. A few days ago, John Singleton, the founder of the company behind RekindleIT, emailed me to let me know that the latest version of the service does the Readability-like formatting I mention above!
I've thrown a number of long-form articles at the updated service and it has handled them perfectly. This changes my whole game. Seriously. Now when I come across an especially long article that I know I'm going to want to read on my Kindle DX, I simply hit the bookmarklet and *boom*. That's it. (Of course, this introduces the problem of there being no non-manual way (of remembering) to link to an article I've just read on the Kindle; on the computer I just use a bookmarklet to jump into MarsEdit.)
Finally, it would be remiss of me to not mention that Instapaper (which I've written about many times before) has been offering similar functionality for a while; however, the key difference here is that RekindleIT lets you send to the Kindle on an article-by-article basis.