Paper from a few years ago comparing Google's OCR system to commercially available benchmarks:
http://www.educatingsilicon.com/wp-content/uploads/2013/10/p...
A lot better for text in photographs. Comparison might be different on dense document text though.
It's potentially a game changer, plenty of industries have piles of scanned documents. Cheap OCR means this data suddenly becomes accessible even if the value per individual document is low (i.e. for input into machine learning).