Product Version = NetBeans IDE Dev (Build 201307202300)
Operating System = Windows 7 version 6.1 running on x86
Java; VM; Vendor = 1.8.0-ea
Runtime = Java HotSpot(TM) Client VM 25.0-b41

Before:
import java.util.*;
class Test<T> {
	static void test() {
		Number s = new Test<Number>().first(Arrays.asList(0)); // Hint: "Use diamond inference"
	}

	T first(List<T> t) {
		return t.get(0);
	}
}

After:
import java.util.*;
class Test<T> {
	static void test() {
		Number s = new Test<>().first(Arrays.asList(0)); // Error: "incompatible types: Object cannot be converted to Number"
	}

	T first(List<T> t) {
		return t.get(0);
	}
}

Same for "T first(List<? extends T> t)".
Works correctly for "<U extends T> U first(List<U> u)".

So in the first two cases the hint should not be shown since the compiler needs this type information.