I have only had sushi from supermarkets (Roche Brothers, Whole Foods, etc.). I like the sushi at Whole Foods, I was just wondering, is there a big difference in taste or quality say from Whole Foods compared to a Sushi restaurant? I feel like a bit of an idiot asking this question but am I missing out?
Yes! There's really no comparison. Unfortunately, there is no universally liked sushi place in Boston. Our favorite is Blue Fin in the Porter exchange in Cambridge. Their fish is excellent (barring a few bad nights, none recently) and the rice is pretty good. I'd stick to basics, nigiri and one or two ingredient rolls for the first time. Blue fin doesn't have too much in the way of fru-fru rolls though. Give it a try and you can see what you've been missing.
(NB this was moved from the Boston board AS I was composing my response, thus the Boston centric response)
I think there is a difference, both in the quality of the fish and the freshness and quality of the rice, and also in the variety of offerings. Once you go to a good sushi restaurant you may be spoiled for supermarket sushi.
I also think that this is probably a topic for the General Chowhound Topics board. Requests for recommendations of Boston-area sushi restaurants are what we'd discuss here. So I will give you such a recommendation: Toraya on Mass Ave in Arlington, opposite Arlington High School. Not high-end like Oiishi or Clio, but very, very good, traditional sushi.
Aside from the initial difference of quality, there's a difference in freshness.
If you have sushi delivered from a restaurant there will still be a fall-off in quality.
Nothing beats sushi freshly made. Even in the time delivery takes, there will be deterioration.