When Mac OS 11 is released it will be a signifigant jump from X. Similar to (although probably nto quite as signifigant as) the jump from 9 to X. The way they have been doing it (10.1, 10.2, 10.3 etc.) when they stop calling it 10 it will be something wholly different (and I imagine extremely awesome). Maybe like those old Knowledge Navigator videos they had. I have heard that 11 will be the next releases after 10.4, but even if that is true I wouldn't expect it for atleast a couple of years after Tiger is released. There is absolutely zero info on 11 right now, so if they are workign on it, it is being kept extremely hush hush.