I always found that the mirror in my GS scope gave me a wonderful view - I do not have my 10" anymore, but that is only because I now have a 12" instead whose view I am even more impressed by. (Keep im nind I have been observing through decent scopes for less than 12 months, I am not an expert at all - I consider my viewpoint may be relevant to your own experience level though).
I have looked through Skywatcher dobs but only in 8" size so I cannot fairly make a true comparison on equal sized mirrors. Others may be able to provide more accurate comparisons re mirrors but I think you will find the quality of mirror manufacturing to be much the same. (Do they all come out of the GSO factory anyway??)
There is nothing wrong with the GSO mirrors, they make a pretty damn good product at a fantastic price. Consider that the Meade Lightbridge range of dobs are entirely manufactured by GSO for Meade, mirror included - they can't be too bad at all.
Keep in mind that there is a difference between GSO mirrors and a mirror manufactured by craftsmen such as Mark Suchting (a forum member) and other professional mirror makers, but with GSO and so on you are getting an entire scope (OTA on dob base), that is very capable of serving many people quite well, for just a few hundred dollars. With a craftman made mirror you are getting a
VERY high quality mirror, but on it's own it will cost you much, much more.
To put it another way: I'd love to drive a Porsche, but I own a Ford - it does what I need just fine at a price I can afford. If I ever decide I need a Porsche I'll just have to save a lot more money first.
(PS: Mark I do hope to be getting in touch
some day, just not this year .. or next maybe... perhaps 2010 ... )
Cheers!