Bumblebee is a way to effectively use nVidia's fucking shitty ass Optimus technology on Linux.
The goal of Optimus was to switch between the integrated Intel GPU and switch to a more powerful nVidia GPU on the spot. While this technology sucked ass on Windows, it was even worse for anyone wanting to use Linux or Unix on their laptops. This is because nVidia completely failed to give two fucks about their *nix users and left them in the dust. While bullshit like this caused Linus to publicly tell nVidia, "Fuck you!", it also spawned an Open Source project called Bumblebee. It was a way of using the Optimus technology on Linux with the nouveau and proprietary drivers. Supposedly nVidia has contributed to this project, but still this shit is ridiculous.
While the fact that Bumblebee is around is great and shows the great side of Open Source, it still sucks donkey dick to use. It makes Linux look like a slow ass broken mess in relation to 3D accelerated programs and games. This is mainly because Bumblebee is not an official project and has some reverse engineering to achieve its goal. Everything is very manual too, having to put "primusrun" or "optirun" before ANYTHING that uses 3D, or your experience will generally be a fucking horrible nightmare from Hell. You can respect what they've done, and they've gotten very far, but in the end you can only do so much with nVidia's terrible Optimus technology.
 What You Should Do
You should NOT get any laptop that has Optimus technology, rather you should stay far away from it and get one that is unfucked. While Bumblebee has improved, it still causes tons of frustration and anger, which will probably lead to you divorcing, killing, and or raping innocent people in an uncontrollable rage from getting Quake to achieve more than 2 FPS.
In other words, FUCK NVIDIA OPTIMUS!