With me it is all about color or about something that really speaks to me. I will pay the premium price for it.
I watch for sales and stock up when I find them in my colors or favorite themes. And I usually end up selling it on eBay when I can't find a use for it. (Or here)
I buy online when it is a fabric that I have seen in a shop so I know what the colors really are. I do this a lot for charm packs. If it is something I am unfamiliar with, I hesitate to buy it because I have made past purchases that were not what I expected when i received them.