Ok, so i'm a dummy :)
The search thing mentioned above wasn't actually working properly it seems and I should have spotted that before I even told anyone about it. Thanks to deepbluesea for letting us know I was being a plank :)
It's working now, I just fixed it - and i've simplified the screen a bit when the username is specified in the URL (ie. there's very little point in asking for a diary title when you're fixed to one username :-) ).
If anybody experiences any issues with it, then as always, drop a note either here or at the support address below ;-)
Matt.