mettelus
Hmmm... So would opening staff view, selecting all notes, deleting them (all), and hitting CTRL-Z work the same way?

Good thinking, Robin! That would be brilliant! I've never had doubling problems, but for the others sake I wish it would work the way you ponder. That would be a superior method compared to any DAW, I'm sure.

Bristol_Jonesey
Another way, although this is a bit long winded (but 100% accurate) is to open up your midi track in Staff View.
 
Any duplicate notes will appear twice on either side of the "stalk" - you can then select one of the duplicates and hit the delete key.

 
I used to use this method, but it's not always easy to identify the double notes.
 

 
 

mettelus
Hmmm... So would opening staff view, selecting all notes, deleting them (all), and hitting CTRL-Z work the same way?

 
A quick test here told me it doesn't work like that. 

i think the cal file Works best.

Oh well, one can always hope (and get squashed like a bug). The Undupe.CAL takes a time window in (in ticks) and looks like it simply deletes repetitions (i.e. all duplicates) of a note which fall in that range window - so is the best method readily available.
 
@Beeps - [FYI - CAL resources to anyone interested] CAL files are text files, so I associated them with notepad so they can be opened/edited freely. Resources are a bit scant now, but there are a few sites that still provide the CAL Programming Guide (CW has moved this file internally, it seems). http://members.ziggo.nl/odw/en/indexmidi.html?/odw/en/CAL%20course.html is the best source that I found recently when building my own.