Anyone have any experiences with the new Mercruiser motor, I've had one on order for 3 months in the UK, but still don't have a delivery date as I'm told Mercury "have issues" with them...

no one?

there are a few on here that have them...hang tight and wait till they respond

If I were you the first thing I would do is contact Merc via email and ask the same question so you have proof from the source.
On a personal note, did you buy from a fully authorized dealer and also did you give a deposit or pay in full? Your dealer may be buying time while he is using your money for other things.(I've been a victim of this)
If there were problems with the 502 I really think it would have already hit the wire here @ good old OSO.

I'm a boatbuilder in the UK, buying OEM from the official UK distributor.

The latest that I've heard is that there is a "field campaign" issued for the motors, possibly due to a problem with a hot start. That is, run them hard, switch off, go to restart them and they suffer internal engine damage, possibly due to hydraulic lock-up.

contact OSO member 509SC on this board (Steve).

He has (2) of the new motors in his new Active Thunder.