A few of UA's IAD flights are on the 767, but most are on the 777.
None of UA 777 have got the business class refit yet - the program starts in September, I think (supposedly the story is that the 777 IFE is driven by a single system, and UA's current y-class seat back IFE in the 777 can't cope with the AVOD so they have to refit y-class on the 777 too, and that requires a reconfig of Y to 3-3-3 against their current 2-5-2).
The new UA business class is OK (as mentioned above), the old business class seat is probably 10 years out of date by current standards - better than anyone's y-class, but not a patch on today's j-class. Mind you, I don't particularly rate AA or CO highly for business class either. Service on UA can be patchy - I [have to] use UA fairly regularly and I find the London based crews in particular are usually fairly good, and fortunately recently most of my flights have had London based crews.
In terms of seats (on the 777) - check seatguru as mentioned before, but business class is split into two sections. I prefer the small cabin of two just rows in front of the number 2 doors (rows 8 and 9 I think) rather than the larger cabin of five rows behind door 2.
Put it this way about UA business... If you get the new seats, all well and good. If you have to pay the same price for UA's old seats as you would have to for business class with BA or VS, I'd probably go with either of those airlines in preference to UA - frequent flyer program notwithstanding. If you're stuck with UA and the old business class seats, its still a heck of a lot better than economy.
Andy