The screenshots that have been leaked so far can be found in the Dota 2 fan website:
http://www.dota-two.com/
I have also posted them below:
According to the website, the screenshots are pretty old and the UI should be vastly improved by now.
Thoughts?
UPDATE:
It seems that the system specs were also released. Here they are:
DotA 2 Minimum System Requirements: (DOTA2 minimum configuration requirements)
OS: Windows ® 7 / Vista / Vista64 / XP
Processor: Pentium 4 3.0GHz
Memory: 1 GB for XP / 2GB for Vista
Graphics: DirectX 9 compatible video Card with 128 MB, Shader Model 2.0. ATI X800, NVidia 6600 or better
Hard Drive: At least 2.5 GB of free space
Sound: DirectX 9.0c compatible Sound Card
Recommended System Requirements DotA 2: (DOTA2 recommended configuration requirements)
OS : Windows ® 7 / Vista / Vista64 / XP
Processor : Intel Core 2 Duo 2.4GHz Memory : 1 GB for XP / 2GB for Vista Graphics :
DirectX 9 compatible with Shader Model 3.0 video Card. NVidia 7600, ATI X1600 or better Hard Drive : At least 2.5 GB of free space Sound : DirectX 9.0c compatible sound card
UPDATE 2:
UPDATE 3:
You can now sign up for the beta at dota2.com



















