Don't have Ebates, but I can tell you from my Upromise experience that more often than not these "portal specific" cards tend to be a PITA.
1) After having the card, you ultimately just start hopping right onto Ebates/Upromise/etc and shopping from there, just assuming it's the best deal, and could be missing out on other deals. Of course some people still compare portals but human nature tends to make us fall into habits. It's similar to people using their CSP to book through the Chase portal regardless of anything -- that "20% discount" can cause you to ignore other options.
2) Cash back tracking is mediocre at best. With Upromise and Ebates seems about the same -- a lot of people have to open tickets to get the missing cash back. I didn't like that hassle. I've used Ebates (not the CC, just the portal) and can tell you that my very first attempt at cash back did NOT work. I didn't bother emailing since the result would have been a small amount of money, but the tracking is far from flawless.
3) If you aren't someone who shops much and don't want to buy things just to buy them (which is good!), the Ebates card isn't going to be that useful. For basic purchases the return is nothing special, and you have to wait for the rewards to "process" on the Ebates sytem.
For loyal Ebates users sure it's a good card and can produce some decent cash back but overall, I'd never apply for a portal specific card again. Too much headache for not enough real gain. Note you can link/use any CC on Ebates/Upromise/etc, don't have to get the portal branded card. Yes you get slightly less return, but if you don't shop much, may not be worth holding the specific card.
OP, don't use a card just to use it. If it truly doesn't fall into your spending patterns, consider moving on.
