People say that, but it's really not. There's still reasonable 4 letter top level domains untaken, and plenty of good names. It just takes some thought, and a fair bit of time.
Off the top of my head, untaken domains:
tweevio.com viotwit.com vitwit.com vittler.com twiveo.com tweeveo.com twoovi.com twoovy.com twitvy.com vidatweet.com vidtwid.com
I'm sure there's tons of better names out there, but I think a few of the above names are 'good enough' to be successful, and best of all, they're all free.
No, the LLLL.coms have been bought up by domainers. They had some crazy bubble (which has now burst) for them as well. There are plenty of okish 5 letter .coms available.
Off the top of my head, untaken domains: tweevio.com viotwit.com vitwit.com vittler.com twiveo.com tweeveo.com twoovi.com twoovy.com twitvy.com vidatweet.com vidtwid.com
I'm sure there's tons of better names out there, but I think a few of the above names are 'good enough' to be successful, and best of all, they're all free.