I am hoping it is mid-March. Having to decided to make the move to Mac in December, it's been painful having to wait. 
I've never owned a Mac, and am waiting on purchasing my first one to replace my desktop PC. I've been following this and other Mac websites for about a year now.
I know historically Mac releases things on Tuesdays. As I read the forums on Mondays, I always (and I mean ALWAYS) see new threads appearing about the possibility of a new release the following day.
Since I've been following Mac, yes releases have come on Tuesdays, but also, there is usually a press show of some kind (notable exception: white mb), to which tickets are sent out 5-7 days in advance.
Does anyone honestly expect a surprise refresh of imacs/minis/pros or is it more likely we'll know a week in advance when they are to appear because of a leaked "Spotlight on..." invitation?
Time to update this thread guys!
Today's rumors basically put more weight on existing rumors, speculation, and evidence:
- NVIDIA graphics
- Core 2 Duo, likely 1333 MHz FSB, 3.0 GHz option
- Imminent release