Could someone explain the differences between these two brake sets? Is there an actual performance difference or is it simply a matter of the BB5 being more difficult to adjust that makes it less popular with many riders? One of the trikes I am considering buying has BB5's and I'm curious about whether I should consider upgrading or not.

In fact I had written a whole big speal but deleted it.
 
BB5s are OEM $$ cut versions.
-The OEM pads wear fast, they are small, they are hard to change, they like to sqeek, they overheat quick because they are small.
-The lack of pad adjustment on the outside makes it difficult to keep up with the pad wear. To adjust you need to unbolt the caliper and realign the whole mechanism. This makes field adjustment very cumbersome or not possible.
-You can potential use the barrel adjuster to attempt and adjust the outer pad but this is just a very temporary solution since there isn't alot of extra pull before the levers hit the bar or the calipers run out of pivot.
 
If I had to guess I'd say I put about 1400 miles on my bb5s. They were good for the first 700 but then quickly became a big pain. I try and ride in all weather, stop hard on steep decents and have alot of weight to stop so I am pretty hard on tires/wheels/brakes.  
 
I think it is all a conspiracy between avid and LBS to make money on upgrading bb5s to bb7s.  
 
$51 bb5s compared to $60 bb7s at jenson usa.  For $18 (front and rear) it is more then worth it. For $120 I'm still happy about it but I wish I could have gotten the bike withough BB5s at all like I wanted.

Excellent information.  I was confused after a conversation I had in the LBS recently. The guy there told me that he wouldn't recommend upgrading because there was no significant difference. That didn't seem to agree with the comments about the bb5's that I was reading from folks who actually own them. Thanks for the help.

I think it depends on the bike. I have BB 5's on the Catrike and they have been flawless for more than 2000 miles. I put bb 5's on the Cafe and they were a total pita from the beginning.
 
Ken