Social media may be alive and well, but some of the most prominent web properties that rose during ‘Web 2.0‘ have seen better days.

From Digg to Delicious, if the rise and fall of companies that were supposed to change the web, if not the world, reminds us of anything, it’s this: the consumer internet market evolves rapidly, and can be as brutal to the losers as it is rewarding to the winners.

But can a Web 2.0 has-been be brought back to life by a couple of entrepreneurs who built one of its biggest winners? Steve Chen and Chad Hurley, who founded YouTube, hope so.

The pair, who sold the world’s most popular online video destination to Google for $1.7bn in 2006, bought the once-popular social bookmarking site earlier this year from Yahoo, which had originally acquired the property in 2005 for a eight-figure amount.

Chen and Hurley’s mission: revitalize Delicious and make it a tasty destination once again.

Yesterday, the company operated by Chen and Hurley, AVOS, unveiled the new Delicious, which looks like a whole new meal:

After acquiring the service from Yahoo! in April, we realized that in order to keep innovating over the long term, the eight-year-old site needed to be rebuilt from the ground up. The result is a new homepage, interface and back-end architecture designed to make Delicious easier to use.
We’re proud of what we built, but the process has also brought the site “back to beta” as a work in progress. Much more work will be needed to realize our vision: keeping the essence of Delicious – the premier social bookmarking tool – while building upon its core functionality to create a great discovery service, too.

The biggest new feature added to Delicious 2.0 is called stacks, which are likened to “playlists for the web“:

Select some related links, plug them into a stack and watch the magic happen. You can customize your stack by choosing images to feature, and by adding a title, description and comment for each link. Then publish the stack to share it with the world. If you come across another stack you like, follow it to easily find it again and catch any updates.

If one thing is clear from the AVOS overhaul of the social bookmarking site, it’s this: Delicious 2.0 is designed for a mainstream audience.

That makes sense given Chen and Hurley’s experience with YouTube, which, along with Facebook, is perhaps the most mainstream of consumer internet startups to emerge in the past decade.

But turning Delicious into a mainstream destination isn’t necessarily going to be easy. Already, many are expressing disappointment, noting that in its drive to make Delicious more appealing to mainstream internet users, AVOS has done away with “a lot of the best parts of the old site” — according to long-time users. Others argue that the site is undercooked and not ready for prime time.

Which begs the question: were Chen and Hurley wise to buy Yahoo’s leftovers, or should they have cooked up a whole new meal?

In the coming months, we’ll almost certainly know the answer to that. In the process, we’ll learn if two of Web 2.0’s most successful entrepreneurs have the Midas touch.