YES! Actually, Siri is a great tool to help enter things like comments into your Diary Entries. You can use Siri as a dictation agent. Whenever you see a keyboard, you can use Siri – provided you have an iPhone 4S.
Just look for the microphone on the keyboard (just to the left of the spacebar). Tap it and then start talking. Whatever you say, Siri will type out for you. It’s actually quite good at understanding the nuances of accents and voices although you may have to correct it now and then. But its still better than sitting there typing on the tiny keyboard.