I've always said pronounced it as the english word. But this is from wikipedia:
GNOME is the official desktop of the GNU Project and the official pronunciation of the name is /gəˈnoʊm/ with a hard G, although /noʊm/ (as in the English word gnome) is also in common usage.
As I understand it, it's "guhnome" just like it was "guh nutella" and so on. There was a time when I could tell you the origins of this pronunciation, but it's been too long since I cared for me to recall
I do get some funny looks from the newer crowd when I call it by its official pronunciation, though.
When I first got started with Linux about 5 years agao, I always assumed that Linus pronounced Linux the same as his name, so I always pronounced it as Lienux....then about three years ago I was watching a web cast that Redhat was giving, and they were pronouncing it the right way, so from then on out, I pronounced it the right way.
For me though gnome with a silent g makes more sense, whether it is right or wrong, as it is more familiar