How do they compare with stores like Target and Costco?
Here's a rant about walmart (which I'll take to be an equivalent of the above):
I decided to try making a poster so I went with WM based on price. Now, I understand resolution perfectly well and I uploaded a file with more than adequate resolution for the target 24x36 print size. Nevertheless, I was given a "low resolution" warning! At this point, I know better than WM's dumb system so I go ahead with the order anyway. In the meantime, as a courtesy, I drop tech support an email informing them about a bug in their system. In short order I get a response back that makes it obvious to me that whoever read my email completely misunderstood it. They didn't get the concept that the problem was clearly on their side, not mine.
The poster arrives and guess what, the quality is in the toilet, massive compression artifacts. At this point I realize their uploader is not to be trusted and I give up on WM and look elsewhere. One place I looked was snapfish whose photo web app looks a heck of a lot like WM's. In fact, it has the exact same bug when you upload large files (low res warning). (It turns out that snapfish has some kind of business relationship with WM) Snapfish, however, has online chat, unlike WM, so I get a live human on the line and describe the problem. I'm then told to use some alternative uploader which apparently doesn't corrupt files the way the main one does (this distinction is of course completely un-advertised). But guess, what? That uploader simply can't handle large files at all (just fails without reporting an error).
I ended up getting the poster made elsewhere (can't remember where) and the results were very good.
So here you have a case of a company (WM and SF) with a product that they can't actually sell (large posters) since they don't provide working uploaders. You would think this situation would interest them, but apparently not based on their tech support responses (I had other interactions with WM on this issue).