I did a test comparing my TomTom GPS TTS against my Kindle 2 TTS. Since I can't load anything for the TomTom to read, I wrote text file with a few words the GPS mispronounced and loaded it onto my K2.
The words were written this way:
405 north toward Santa Monica
Los Angeles
The results were:
405 (Angelenos pronounce it 4-oh-5, GPS pronounced it 4-west-5, K2 pronounced it 4 hundred and 5)
Santa Monica (GPS was correct but it sounded weird, K2 said "Santa Monica Los")
Los Angeles (I can't begin to replicate the way GPS mangled it, but K2 missed the "Angles" part as you see above)
Not all TTS is created equal.