For me, the biggest issue with Peak 4.1 is that its such a cpu hog. Earlier versions crashed merrily, after messing with your files. Not such a problem anymore, but the way it uses resources is obscene.
Peak is all aqua'd out, and probably does all its graphics through calls to the API, the way Apple wants. This creates huge demand on resources, making it less than certain that real-time application demands will always be met.
In other words, with Peak I get way too many drop outs on DAT transfers.