A local company had a number of 2TB USB 2.0 WD external My Book external HDs on sale for $79.95, so I bought one because the price was too temping. I thought I'd repartition the drive so I could haVe a part for Snow Leopard, one for ML, and then a few more for TM backups off my main system. I use SL once in a while for some older PPC graphics apps. In any case, after I put both SL and ML onto the thing I decided to boot off of it. I wasn't expecting Ferrari like performance but I wasn't expecting errors, either. What happens seems to be that the drive just plain locks up once in a while. You'll be in the middle of something and it will just freeze. I thought the drive was bad so I got out my copy of Scannerz and ran a scan on it. The drive ****looks**** like it's passing with one strange caveat: Randomly, Scannerz picks up a long irregularity, and it's ALWAYS, not sometimes, ALWAYS 30.5 sec +/- 0.15 seconds. I couldn't make sense of the problem. I contacted SCSC (who makes Scannerz) and they had me send them the log file for the test. They said they're going to try and get a unit like mine to replicate the problem, but indicated that it looked to them like the drive was either falling asleep or parking its heads....right in the middle of use. Has anyone else ever had this problem? I did a little research and this external unit and it's using a some type of variable spindle speed Western Digital "Green" drive. This is a Western Digital My Book for Mac, USB 2.0 unit 2.0TB Units. As-is, the unit is almost useless to me. The sole purpose wasn't to just do back ups, it was also to be used to host a clone of both my SL and ML partitions, and allow me to eventually pull the SL partition off my internal HD all together. And low and behold...I bought it 35 days ago so I can't return it.