The downside to Bluetooth is the price of components. Expect to pay at least 30% more for a Bluetooth version of the same item, compared to RF or IR. Many of these come with their own Bluetooth USB adaptor (also doubles as charger), which would be a waste of money if you had internal BT.
I just picked up the card for my i9200 from spare parts, and it installs in seconds. But with the price of add-ons, I'll probably wait to get BT mouse or other.
At first you imagine the possibilities, like BT enabled Headphones (not mono headset), FF Steering wheels, joysticks or gamepads, speakers, GPS, then reality sets in when you see little to none is offered, and what is available may not work, and is way overpriced. Hopefully this will soon change. Then there is the Bluetooth standard. Currently our internal is 1.1, yet 1.2 is out now in some forms, and is supposed to be the fix for the above type devices. Will this be like USB 1.1 compared to USB 2.0? Will out internal 1.1 BT be outdated in 3 months?