The lack of consistency has gotten worse with apple in the last few years as iPad iPod iPhone have grown much faster then apple computers have grown.
I had a similar issue with my 2009 MBP, the funky SATA controller freaks out with some HDs - notably the WD Scorpio Blue - with constant beachballs etc.
I had good results with the Seagate Momentus 500GB and the Hitachi 500GB 7,200rpm drives and both get a 3GB link speed. Apple never really resolved that issue, related to the firmware 1.7 update. Many people had to go back to 1.6 just to get a working machine, and that dropped the link speed down by half to 1.5GB.
Another example of sloppy work on Apple's part, and I too think that was a result of the company paying too mauch attention to the new products, reducing their capability to maintain excellent quality control.
BTW, this new Mac Mini screams, just converted an album, James Vincent McMorrow's excellent Early in the Morning, from Flac to mp3s. It finished the whole album while I was making a folder to put the files in and I thought the app had crashed 'cause the window was blank (it empties the window when all the files are converted).



So I am not so concerned about the slow HD. I will put a WD Scorpio Black in there when the price drops back down (After the Flood).
And surprisingly enough, Lion seems a bit more stable than the various posts have suggested (probably just not running into the problems lurking in the shadows).
I have found that one app I use often, SilverKeeper, is a little funky under Lion, have to restart it half the time, so I'll be looking for a replacement app.
Otherwise it is working fine so far.
In contrast my MBP running SL refuses to allow File Sharing in the Sharing Prefs Pane!
Can't figure this one out.....

Thanks for the comments.
