Well, I finally got to UBurger this evening, although honestly I hadn't been planning on going there (plans I had in Kenmore Square were canceled). Anyway, it was pretty crowded when I got there, but emptied out a bit just as my order came up, so I was able to grab a seat.
I went for a basic cheeseburger cooked medium well (I know, I know), and an order of fries. The burger was very nice--griddled to perfection, with fresh, tender beef and cheese on a basic bun. I thought the fries were better than the burger, though, as they were heavily salted, fried enough so that they were brown and crispy, and it seems like they were handcut as opposed to being out of a box.
I think tamerlanenj called UBurger a high-quality fast food place awhile ago, and I would probably have to agree with that assessment. Nothing spectacular, but a terrific alternative to McDonald's, BK, etc. Prices are a bit higher than those places, but still pretty cheap at $4 to $6 for a burger.