Web2.0 throws up so many new ideas at such a furious pace, it’s simply amazing.
If you’re feeling too proud of your abilities to write web applications, you sure should check this out:
Do a web search for “The Top 100 Alternative Search Engines“.
Mind you, this list is only search engines!
IMO, if you are serious about emulating/improving any of those ideas/sites, the correct ethical and least-effort way is to join their respective teams with quality add-ons or features, and not compete by copying – that is thievery.
And for good measure, copying of ideas from someone and making a program is now becoming an offence that can get you extreme penalties.
So watch your step carefully.
But those search engines are definitely worth looking at, at least once.