Apple's always been known for its amusingly-conservative disclaimers (you can't use iTunes to "design a nuclear weapon," for example) and it looks like the products-liability team at the Fruit has had their way with the iPhone SDK agreement as well, inserting a provision specifically prohibiting developers from creating apps "marketed for real time route guidance; automatic or autonomous control of vehicles, aircraft, or other mechanical devices; dispatch or fleet management; or emergency or life-saving purposes." Yep, that's right -- no real-time route guidance (or, uh, fleet management) allowed. That'd be a huge bummer -- except, of course, that TomTom has already come out and said that its app is ready to go on the iPhone. Assuming TomTom used the SDK and not the jailbreak toolchain, we'd bet that Apple is just covering its ass here and that it's worked out an agreement with TomTom to pass along any liability -- you can bet Steve doesn't want to get sued when iPhone users start careening into sandpiles and into oncoming trains. We'll see for sure when the App Store finally launches, though -- until then, it's all just cheap speculation.
Update: Astute commenter Austin points out that these terms are copied almost word-for-word from the Google Maps API terms -- which means that TomTom and others are probably free to use their own maps to do real-time guidance.