Maybe I'm just making excuses for my daudling, but one reason I've gotten hooked on World of Warcraft and maybe now EVE Online is that I think that social software like Delicious has a lot to learn from MMORPGs.
Someday, I might write something more in-depth, but I don't know if I have a ton of interesting or original ideas or conclusions yet. There are undoubtedly smarter people who offer more articulate theses than I will.
However, one difference between WoW and EVE that I'm thinking about right now has a lot of bearing on Delicious. I'll take a few minutes to do a brain dump on that here.
WoW splits its community into isolated, sharded realms as a way to handle scaling in both content and hosting resources. There just isn't enough room to play in Azeroth and the Outlands for 8 million or so people all at once - they'd be packed shoulder to eerily pass-through shoulder. Even if Blizzard could support that kind of crowd in one realm, it wouldn't be any fun. Thus, the realms infrastructure accounts for both technological and (virtual) spacial limitations.
On the other hand, EVE has found a way to host players all in one common space with natural fuzzy separations between clusters of population. In EVE, space is big. Really big. You just won’t believe how vastly hugely mind-boggingly big it is. (Thanks, Douglas Adams.)
Furthermore, EVE space is mostly empty, only sparsely populated with player and non-player content. There's no need for meticulously artisan-crafted Azerothian terrain between the stars beyond the collapsed wormhole in New Eden. In fact, EVE could conceivably expand its universe procedurally like its spiritual ancestor Elite — which fit 256 complete and rich star systems into under 64k RAM in the 80's. Of course I'm sure there's plenty of human creativity going on in EVE, but there's a force multiplier available.
Following from this, the aspect of EVE I find interesting for Delicious is how the universe itself tends to keep players from bunching up — a feature I'd guess helps in maintaining the hosting infrastructure and in keeping things fun. Travel throughout the EVE universe is free in terms of money and hardfast restrictions — but it is time-consuming and disincentivized by dangerous neighborhoods placed along the way.
Thus, rather than requiring a paid character transfer (US$25) laden with caveats to get closer to friends and interesting things, EVE just demands an investment of time and in-game risk. Of course, this strategy fails occasionally in EVE — consider the Jita system, for instance. But, the overall one-world-ness of EVE is amazing.
So, given all this, I don't yet have any conclusions. But, think about Delicious: Our game space encompasses the whole of the web and everyone in it. Considering the structure of EVE space, how could the fabric of Delicious space be scalably constructed so as to encourage personally-rewarding relevance in communities clustering around interests — while still allowing free travel between haunts? Oh yeah, and a few favorable hosting characteristics would be a nice bonus too.