Doesn't have to be Centrino. Most of today's laptops have Wifi built into them, Centrino's just a marketing name for the Pentium M+Intel Wifi combo.

Unless you're doing very highly specialised computing intensive work (3D modeling, video editing etc.), most of today's laptops are at par with desktops when it comes to power. I still prefer the desktop because it's very comfortable computing if you set it up right, i.e. desk, chair, monitor, keyboard, mouse, but the laptop's mobility can't be beat.

It depends on your purposes, really. If you just need a computer, a desktop would be cheaper and a lot more comfortable, but a laptop's very convenient to have,