You often read that people do not really need more cores because the existing software hardly makes use of those extra cores. While this is increasingly not true in itself, it is absolutely untrue in BOINC, where every core counts. I will show you some scores for octo-core Bulldozers and Piledrivers, compared against hexa- and quad-core Phenom II's and a quad-core Athlon that most of you will still be using.
As with the quads I will break it up into project categories, starting with the Astrophysical ones (A. Because the 'A' comes first in the alphabet and B. Because WuProp has these values complete, unlike some other categories).
Two first value is the maximum per core per day, the next is the value per CPU per day, multiplying the scores with 8 for octos, 6 for hexas and 4 for quads.

1: Astrophysics
Project Name Athlon II X4 640 Phenom II X4 965 Phenom II X6 1055 Phenom II X6 1090 Athlon FX-8120 Athlon FX-8150 Athlon FX-8320 Athlon FX-8350
Asteroids
1,040/4,160
1,286/5,144
1,078/6,468
1,241/7,446
878/7,024
987/7,896
1,527/12,216
1,108/8,864
Constellation
592/2,368
709/2,836
575/3,450
650/3,900
466/3,728
492/3,936
814/6,512
747/5,976
Cosmology
904/3,616
658/2,632
706/4,236
996/5,976
549/4,392
553/4,424
715/5,720
853/6,824
Einstein-(SSE/SSE2)
823/3,292
843/3,372
787/4,719
917/5,502
505/4,037
843/6,740
na
ub
Seti
654/2,616
1,235/4,938
1,006/6,033
1,389/8,334
514/4,109
921/7,371
680/5,436
867/6,932
na= Not Available
ub=unbelievable (as in too high to be true)