I've added about 10 computers with the same account ID to BOINC and recently went to my account info to check their status. Most are windows, a couple are Macs.
All were added around the same time, and I'm sure that they have all recieved, processed and uploaded a number of completed workunits. However, only one computer seems to have any credit assigned to it (the one at the top of the list). The others all list zero. Interestingly, browsing the account details of several other users reveals the same symptom. Is this a bug at BOINC's end?
It is most likely just a coincidence. I did notice one thing looking at your computers. The one that has credit is most likely turning in twice as much work as any of the others so it has a better chance of getting credit granted.
Two of your computers now show granted credit. All of the others except for the AMD Duron and the PowerBook show "pending" credit. (click on the computer host ID and then select results from the bottom of the host info page).
For the Duron, in the first tab of the window, right click on the project and select update. It is still processing on its first group of downloads. Selecting update will allow the pending credit to show for completed units. On the PowerBook you will need to end processing in the terminal and then restart with the update flag, as follows: ./boinc_3.18 -update_prefs http://setiathome.ssl.berkeley.edu/
"boinc_3.18" will be the full name of the BOINC as it is on your computer. I shorten the name on mine for convenience. It looks like the PowerBook is the slowest of the bunch, so it will take a few days for it to crunch through all 8 of its initial work units. When it goes to connect again to download more units, then it will register the completed units, and will show either granted or pending credit.
Before "granted" credit shows, the work unit must be "validated" by two other computers, then the median claimed credit will be granted to all three. Some of your completed work units have not been validated by any others yet, and some have been been validate by one other computer. As soon as they are validated fully, you will receive credit.