Not so much for the PS3. Sony recently halved the cost of the PS3's development kit, but buzz from developers inside is that the PS3 is just not worth the time, at least on initial release, to focus on when the 360 developer kit is more user-friendly.
Also, though the PS3 has more processing power, games on the 360 usually have higher FPS and people say they look better. Some problem with the way the CPUs handle their processing jobs. Xbox 360 is just the best.