If you really really want the item, and you're going to be around to snipe it, then go for it.
I personally dont do it, but I probably would if it was like a once in a lifetime thing or something that only came up very very infrequently on eBay that I just had to have. I'm not really that way about things on eBay though. I'm more into things that there always seems to be a couple of all the time.
The day I start bidding on the rare, aka expensive, stuff is the day I unplug my computer and quit working here