Snow Leopard was 10.6.5 thats why it wasn't a new cat it was a Snow Leopard instead of a Leopard because it was a part of the Leopard release.
Next one will be a completely different cat.
Based on Apple's release schedule for Mac OSX....it should be in about 2-4 years before 10.8 comes out.
Call me pedantic but I just have to correct you on this.... Leopard was 10.5 and Snow Leopard was 10.6, not an increment to the Leopard version number.
The below is from Wikipedia
Rhapsody Dev Release codename Grail1Z4/Titan1U
Mac OS X Server 1.0 codename Hera
Mac OS X Public Beta codename Kodiak
10.0 release codename Cheetah
10.1 release codename Puma
10.2 release codename Jaguar
10.3 release codename Panther
10.4 release codename Tiger
10.5 release codename Leopard
10.6 release codename Snow Leopard
10.7 release codename Lion
So, as you can see, Snow Leopard wasn't a 10.x.5 release it was in fact an major increment as per all other OS X releases.
Yes, I'm a pedant
😛