I've used the availability as a means to gauge how much I want something. If I see something, agonize whether or not to get it for too long, and then realize that it's gone.... THAT is the time I sit back and ask if I'm disappointed or relieved. If disappointed, I'll know to jump the next time. If relieved, then I've saved myself some buyers remorse.
Granted, nobody knows how long you'll need to wait for the next opportunity. I missed out on a Mac Mini to use as a media centre, and had to wait almost a month before I saw it again. Boy, was I all over it when it popped back up again.
I've also found that the five Macs I've ordered through the Refurb store ship very fast (out of Cali), and arrive within 2 days of my order. YMMV.