I just installed an xp-120 with that panaflo fan. I dont have any vibration issues at all. I have my fan at blow, and the only time there was any type of vibration was when i put my hand in fron of the fan, there was a little buffeting noise, so maybe it has to do with limited airflow is peoples cases.
I plugged the fan into the mb, and I use a program called speedfan, you can set teh max and min speed you want the fan to spin at. At 100% i must say the fan is a little loud for me, but at 80% is it prety quiet. I have my min set at 25% and it stays aroudn there most of the time being super silent. my temps so far are 32 deg idle, and 43 load. That is even with the fan not spinning up to 80%. My temps might be skewed because i live in a crappy college house and my room is pretty cold lol. So far not knowing what the rpm's are hasn't been an issue for me. Make sure you dont set the min on speedfan too low though, or the fan will stop spinninig. I scard myself yesterday when i looked in teh case and the fan wasn't spinning, I freaked out but i cheked my temp andmy idle was at 40. the xp-120 kicks butt.
Overall I'm very happy with the fan and I highly recommend it. At max speed it pushes a lot of ait, and at lower speeds the sound is pretty quiet.