personally i think it is stupid.
I agree with the concept of being able to just continue typing, rather than having to send part of a message, then type and send the second etc.
But surely they should tell you you are starting a second, third etc message!!!
My Sony Ericsson k700i tells me when i am starting a new message, and I am very glad that it does!
Sorry - I am not a nokia fan to say the least, but that argument has been done to death, so i wont continue :)