It is interesting.
My point though is that Google has to find you. It can find you by you directly submitting your URL and then Google goes off and crawls your site.
Or you can use a bookmarking site and wait for Google to find your link on it (and you have no guarantee as to how long that will be) and then it goes off and finds your site, crawls it, indexes it and we are at the same point we were at when Google crawled your site after you submitted your site directly to it.
Whats the difference, the only difference is the method of how Google becomes aware of your site? Assuming all other things being equal.
Just I prefer to have as much control over how my site is indexed and prefer not to leave it up to those who have no good reason to be concerned with it, and when I say that I mean bookmarking sites.