Miguel asked if there was a limit to the number of simultaneous Netflix streaming titles you could watch, and according to the Netflix website the maximum number of streams depends on your unlimited plan:
Some membership plans allow you to watch simultaneously on more than one personal computer or Netflix ready device at the same time. If you are on the 1 disc out at-a-time plan, you may watch only one device at a time. If you are on the 2 discs out at-a-time plan, you may watch on up to two devices at the same time. Members on the 3 disc plan can watch on up to three devices. The maximum is four devices simultaneously, and that is available for members on the 4 or greater discs out at-a-time plans.
I was able to get 3 Netflix-ready devices (Mac, iPad & Roku Player) playing the same episode of Mythbusters at the same time on a 6mb DSL connection:
There is also a limit on the number of Netflix-ready devices you can activate per Netflix account: 6. If you have more than 6 devices like me (I test a lot of different Netflix-ready devices), you can deactivate a device and enable a new one.
Have you hit the streaming or Netflix-ready device limitation?