Warranties are different (longer, in some cases) among brands. eVGA has an excellent step-up program and they'll allow you to replace a card even if you've damaged it due to overclocking. XFX does that as well. I voted yes. Brands are important with regard to GPUs.
For most products in general I don't think brand is important, but from working in a computer Service Department I do believe it is important (for the most part) with electronics. You get what you pay for...ie how many crappy 39.99 Planet routers were returned when we should have been stocking only D-Link and Linksys. Because this is a computer forum, I answered Yes, though for most other thing in life I would answer No.