Is twitter valuable as a brand (lot of stink there) or merely for its installed userbase (the more valuable of which will probably stick around as moving is hard) and maybe a bit of tech (building a twitter clone is trivial, solving some of the problems with mass scaling of such things* is rather more annoying)? He was pretty open about it being largely for the latter to shortcut growth on his equivalent of some of the Chinese offerings (some of those starting out as instant messenger things and blogging/forums and now being the default payment method for most of the population, skim a bit of that as a transaction fee and the weed themed billions he offered will look like one of the best investments in history).
*building something equivalent for friends and family that could go down for a week without too much hassle and run on a $100 a year shared host is nothing, however start splitting the database from the server and you have lag there, furthermore lag if you then put a copy on each continent/major area to dodge lag and backbone bandwidth, possibly deal with international censorship (and internal censorship from within), and seamless backups (one hard drive might run for 20 years, 10000 will see one fail possibly on the daily) and and and and... that is a real trick and mostly born from pain and experience in the specific role you care about.