Works flawlessly with the built-in BT device in my laptop, sorry it doesn't for you.
EDIT: What version are you using? I was using 0.6.0005, but thought I'd try updating to the latest version (0.7.1000), and doing that promptly made BT connectivity stop working. Uninstalled it (and the drivers), reinstalled 0.6.0005, and now everything works great again. I read on the MiJ forums about people having the exact same issue with the latest version, so maybe try 0.6.0005 if you haven't?
Assuming you're using it for PC games and not just emulators, you will eventually run into issues mapping the ps3 buttons to xbox 360 layouts. (since most PC games default to this and offer no alternatives) There is An option to emulate xbox templates within motion joy, but then when you get the on screen button prompts they willusually be xbox button icons. It's just a headache imo, just grab a wireless 360 adapter off Amazon, plug and play.
Huh, what mapping issues? You just set MotioninJoy to emulate a 360 controller, and the mapping is done for you. Works flawlessly, and the button layouts match 1:1. The only very tiny "issue" can be with games that don't let you swap the functions of the bumpers and the triggers (which you obviously usually want to do when using a PS3 controller, at least in games where there's shooting going on), but that is super-easily fixed by swapping those mappings in the MotioninJoy settings instead.
Yeah, you have to get used to pressing X when you see an A prompt, etc, but that's really not very hard (especially if you've ever actually used a 360 controller). I got used to it very fast, and it's not like you look at your controller when playing anyway.
So nope, not getting the issue. I've been using a DS3 as a fake 360 controller for PC gaming for well over a year now, and it works extremely well for me.