The Treo 650 clearly and consistently indicates what mode the keyboard is in. In the lower left of every window, there's a symbol for shift (arrow), caps lock (underlined arrow), num/symbol (circle), or num/symbol lock (underlined circle).

This has been carried forward to the Pre, perhaps more clearly yet less consistently. It shows the symbol right near the cursor, bringing it closer to your attention.

Unlike the consumer-grade phones which don't care to preserve consistency of input and OS through the years, the Pre keyboard is very familiar to Palm users and the drastically advanced OS has even maintained some similarities. They make the transition, and user retention, easy.