15 years later, Facebook brings in $3.2 Billion in revenue and has a market cap of ~$41 Billion, or about 12.8 times one year's revenue. [2]
And we won't mention Google, despite the fact that they're the most obvious tech company to compare the likes of AOL to, because they make more money than God, and it would harm the argument. Uber, Twitter, etc. may be overvalued, but they bring in cold hard cash, and they're barely getting started.
Things are frothy right now, for sure; there are some really high rounds being raised that are justified by portfolio theory, and some no-product seed rounds at really high valuations. There will be some major catastrophes, and people will lose a lot of money.
But I have no idea how Cuban could possibly make the argument that it's worse than 1999.
[1] http://en.wikipedia.org/wiki/Mark_Cuban#Business_career [2] http://ycharts.com/companies/FB/market_cap