O Brave New World...

*is reading through some old entries and commenting since you're a new LJ friend* FWIW, I looked at the site and tried some of the tests, and wow. I'm not fluent (yet) but usually (at least to me) the differences between the dental and retroflex sound a lot more distinct. That could also be the accent, though--my lecturers were both from Rajasthan and I could hear that they had accents (or at least I could tell that sometimes they pronounced things different from the Devanagari).