Just a thought
if i bought by DOpus 9, would that entitle me to DOpus10 ??
was just thinking
thanks
The point updates tend to be free while the major updates tend to be charged for. However if you buy 9 just before 10 came out I think they will let you update to 10 for free. I don't know what the time frame for this is though.
I think that was the case for 9, i'm sure someone else will come by and confirm this for you.
What Reck says is right, at least judging by the past.
Whether the next major update is handled the same is up to GPSoftware and hasn't been announced. Opus 10 itself hasn't been announced yet, either, of course. 
Although loads of features and changes have been added since, the last time existing users were charged for a new version was when Opus 9.0 was released on 28th April 2007. This was the deal at the time: