Friendster. With better architecture they are sitting on billions and Mark Z is writing code in a cubicle at Google...
There were guys in Columbia university who (supposedly) had a much better system than Mark Z, and are probably writing code in a cubicle at Google or equivalent.
I suppose Zuckerberg got his start because he knows how to code, but he is an excellent CEO, something neither of these 2 guys nor Friendster had. Do you really think facebook is winning because of a better architecture?
I despise facebook, and don't use it. But I recognize that Zuckerberg has been doing an excellent job in growing the company, seizing opportunities, thinking huge, and most importantly -- bringing the right people in at the right time.
I tend to agree with Fred Wilson about the three things a CEO does: develop vision, acquire talent, raise money. Zuckerberg has done all three very, very well.
In implementing Facebook, Zuckerberg redefined the problem space to give him an implementation advantage at every turn. Limiting it to manually-added colleges didn't just restrict the total userbase to be manageable -- it also introduced the concept of 'networks' that mostly eliminated the graph traversal problem. Photos were severely limited for a long time to constrain the storage problem. They also had a massive advantage in that they came of age in the post-bradfitz era of big consumer webapp architecture.