Ya... and Amazon almost certainly has more than 3000 TB of storage (3 PB).

Hell, they've got pricing tiers for S3 customers that go up to 5PB.

that's the part where I tried to show that I was absolutely being sarcastic. :/

I was being so extremely sarcastic to show how ridiculous it is to say "harder to scale than Twitter". Of course there are nowhere near 175 million users, of course they don't tweet ten tweets per hour, and of course the tweets aren't uncompressed. My point is that even with all these assumptions, you have a ridiculous lack of scaling problems. My mention of amazon was meant to show that I was absolutely 100% being completely sarcastic when talking about Twitter's "scaling" problems.