iirc, RtlCreateUnicodeStringFromAsciiz has a limitation due to use of the UNICODE_STRING structure - it can only deal with strings up to 2^16-1 bytes in length. Input to edit controls and other strings may be longer than that, so be careful where you use it.
It also makes our DLLs depend on ntdll so we can't drop them into a Win9x install, I guess.
Not sure if we care about that though.