Well I wrote the JasperReports book with version 3.6.0 and one of my colleagues tried all the recipes with 3.7.0. He reported only minor problems while working with 3.7.0. In our company we are still using 3.6.0 and I don’t think it is worth shifting to 3.7.0. I guess there are some features and bug fixes in 3.7.4 but I haven't tried anything after 3.7.0.
The later versions have some back-compatibility issues too. The same files which had worked in earlier versions will generate compile errors in later versions like 3.7 !! Even upgrading from 2.x to 3.5 was a hassle.