IPhone :: IMessage Is Slow, Receiving Messaged 12 Hours Late?

For the past 3 or 4 weeks mine and some of my friends have been noticing problems with iMessage. We will send an imessage and either it will not send, or it will claim that it was delivered when in fact it was not. These messages do eventually get through, but normally seem to come through at 4-5am which is incredibly annoying. I assume this is a problem with the apple servers, as text messages work fine. All other forms of data transfer are absolutely fine too. This is very frustrating as i purposefully got a small number of texts on my phone contract as I assumed i would be able to use imessage for all my messaging needs. I have a iPhone 4, with the latest update (5.1 i think).