other than the general concensus that it was a pain to fly (VERY sensitive on speeds, especially on approach) and quite underpowered. B-47s used to use JATO units in order to get off the ground on less than a couple miles of runway. That makes for a pretty expensive takeoff. The B-47 also only had a 3 man crew (compared to the B-52's 6 man crew), making for a very high workload, especially for the guy in the nose.

B-47s were the reflection of aeronautical engineering for their day and were beautiful machines. Here are some interesting comparisions between a B-47A and a B-52H, just to show what progress was made in about 11 years.

B-47A:
First Flight: Spring of 1950
Engines: 6 J47-GE-11, 5200 pounds thrust each
Max TO Weight: 162,500 pounds
Max bomb load: 22,000 pounds
Range: 3000 miles with 10,000 pounds bombs
Max speed: 617 MPH @ 10,500 feet
Cruise speed: 486 MPH
Ceiling: 46,100 feet

B-52H:
First Flight: March 6, 1961
Engines: 8 P&W TF-33, 17,000 pounds thrust each
Max bomb load: 70,000 pounds
Max TO weight: 488,000 pounds
Range: 8,800 miles max, 4300 mile combat radius w/o refueling (bomb load unspecified for these figures)
Max speed: 650 MPH
Cruise Speed: 530 MPH
Ceiling: 47,700 ft at 306,350 lb combat weight

So, in the span of 11 years, we increased the max takeoff weight by a factor of 3, the max bomb load by a factor of a little more than 3, the max range by a factor of 3. The B-52H also cruises about 50 MPH faster. Not too shabby. Now, if you really want to see some interesting comparisons, look at planes that first flew around 1939, like the B-24 or perhaps the B-26. Talk about progress! The B-47 was a huge increase in performance over those earlier planes, just as the B-52 was a huge increase in performance over the B-47. Too bad things have pretty well stagnated since then.