Can Web 2.0 stars get a second chance at success?

When social-bookmarking pioneer Delicious arrived with a new design and the beginnings of a new service, it wasn’t just a significant moment for the site’s fans and critics. Sure, the purists might not be happy — a number of features seem to have disappeared — and there’s always the chance it could revitalize a brand that has looked unloved for a long time. But it was interesting in broader terms, too.

What makes the return of Delicious really fascinating to me is that it’s the latest sign of a resurgence in activity by some of the people who were the earliest pioneers of the social-web boom, back in the middle of the last decade. Delicious, after all, is a former “Web 2.0” staple that’s being regenerated thanks to the work of two other prominent Web 2.0 founders: YouTube’s (s goog) Chad Hurley and Steve Chen.

And the relaunch is timed, coincidentally enough, just as another Web 2.0 veteran — Flickr (s yhoo) co-founder Stewart Butterfield — also returns to the fold. Tuesday sees the public launch of Glitch, the cute, massively multiplayer online game he’s been developing for the last 18 months or so — a sort of surreal Mario-meets-World of Warcraft. (Disclosure: my girlfriend works as a contractor on Glitch, and I count a substantial portion of the team members as friends).

It’s not just a return to the front line for Butterfield, but also to Flickr’s roots. The photo-sharing site started off, after all, as the offshoot of a project called Game Never Ending. Watching these two moments is a bit like a flash back to six years ago, when the bright young things of Web 2.0 were starting to assert their influence over the future.

Welcome back, class of 2005

Six years ago, there was a crop of audacious founders who made their names cashing in and setting the Web 2.0 boom into motion. In the space of just a few months, Rupert Murdoch had purchased Myspace, Skype was bought by eBay, (s ebay) and Yahoo had gone on a spending spree that resulted in a dizzying sequence of purchases: Delicious, Flickr, MyBlogLog and more. These were all big bets, not least at Yahoo — which looked as if, for a while at least, it might use those deals to create the core of a new, faster company built around social information.

There’s no doubt that this group of entrepreneurs, whether they sold their businesses for millions or billions, were ahead of the game. Today, the ideas they laid out are writ large across the web: YouTube is even more enormous than it was in the past, trading links has become a real core of online activity, and no site would seriously consider launching without social elements.

But ever since its companies sold, 2005’s graduating class has seen the direction and shape of the web move away from them. Essentially, as Facebook rose, so their influence has faded. And so now we seem them attempting to come back and prove they can do it all over again: There’s Hurley, Chen, Butterfield. There’s Caterina Fake, Flickr’s other co-founder, who is currently hard at work on a new stealth startup called 2bkco (see disclosure). And while Delicious founder Joshua Schachter might not be involved in the new version of the site he created, he’s running another company dedicated to making social software more useful.

Beyond building things they like, what is it they are all trying to do? Do they want to claw back some of that influence, or prove that the ideas they had in the past are still important? It’s hard to say. Certainly, they are all more than simply lucky, because they are clearly talented people. But here’s the thing: the web looks like a very different place today than it did back then.

In reality, the company each of these entrepreneurs probably thought they could build is what we know as Facebook. But the Facebook of today is a radically different kind of service than the one they imagined, and it’s native to a different kind of web than the one inhabited by Delicious or Flickr or any of the others. It’s rapaciously hungry, unashamed to force us to behave in particular ways — and prepared to collect an overwhelming volume of data to get what it wants.

Sometimes it feels as if the early social sites are like internal combustion engines, purring away happily while Facebook powers up like a particle accelerator. And that’s why it’s important for this returning group of entrepreneurs to do more than simply bring the ideas they had in the past back to life.

Silicon Valley is populated with people who got lucky once and cashed out, usually thanks to the largesse of a free-spending major corporation like Google, Microsoft (s msft) or (now) Facebook. Many simply disappear with their winnings and are never heard of again. Others return with new ideas and new companies. Why? Partly because that’s the only thing they know how to do — and partly because they want to prove that they weren’t just fortunate, they were good. And that’s the challenge facing this latest crop of success stories, too. How they fare remains to be seen.

Disclosure: 2bkco is backed by True Ventures, a venture capital firm that is an investor in the parent company of this blog, GigaOm. Om Malik, founder of GigaOm, is also a venture partner at True.