check out: http://fontfeed.com/archives/the-logos-of-web-20/

Great article - thanx Simon! No Twitter font listed there though. Someone has suggested, and I tend to agree, it's a custom job.

it sort of looks custom... maybe try posting the question on that fontfeed acticle...

It's probably custom indeed, and in my opinion it's rather poorly done too.
I mean, what's up with that first 't'? Is it somekind of capital? It's all big and fat. The other two 't's are also much too heavy. The 'e' is just a blob.