Yes, it is reliable, and you don't lose any performance.
Boot Camp is Apple's implementation of a dual-boot system, so Windows is not set up differently than OS X on your machine. They exist in parallel, on different partitions, similar to when you install Linux beside Windows on a regular PC.
If you're running Windows via Boot Camp, there is no OS X running in parallel. That's only possible with virtual machine software, such as VMware Fusion or Parallels, and with them you lose some performance, especially in regards to graphics, e.g. gaming.
Any specific performance problems are related to hardware drivers in Windows, not Boot Camp (as a technology) itself. You'll use the Apple-provided drivers for almost everything (except maybe graphics), so that could be an issue similar to any other hardware you're using on Windows.
Drivers (and their problems) are model specific, and I don't have the current MBP model, so I cannot say how well they work. Consider looking up your particular model in Apple forums or other discussion sites and see what others are writing.