Note: iSites (drop boxes for assignments)
Harvard courses accept uploaded assignment submissions through a system called “iSites.”
Our iSites site is here:
http://isites.harvard.edu/icb/icb.do?keyword=k64647
To log in, you normally use a Harvard University ID (HUID), which is supplied Harvard Extension (see http://www.extension.harvard.edu/2009-10/register/guidelines/ids.jsp).
The login button is in the upper-right corner.
After logging in, you will see a dropboxes item on the left (see screenshot below – I’ve added an arrow). After clicking that, you should see a dropbox into which you can upload an assignment submission.
Note: I’m not sure if Harvard has completed our site, so the dropboxes may not work yet.

Looks like this isn't working yet. It didn't ask me for an HUID, and "Drop Boxes" is a mostly-blank page.
(Either that, or it isn't playing well with my browser.)
@Ron Newman
You should see a "login" button in the upper-right for the page.
D'oh! Missed that entirely -- it's in a really obscure place.
This might help someone... If you are a brand new student like me, you'll have to use your HUID (Harvard U. ID) instead of the DCE login ID (looks like @########).
The DCE ID was e-mailed when you first registered for the class. The HUID may have been mailed to your home address on file.
If you don't have it, you can find it by logging into the Extension School with your DCE login.
There, click on "Personal and Computer Account Information", then "Check Computer/E-Mail Account Access", and finally choose your term. Your Harvard ID will appear in the upper right.
Then you can go to the Harvard Pin website to request a pin for your account. Click on "request a new pin" allowing you to create a password for your 8-digit HUID number.
Just curious - is the 'View Details' link supposed to do anything useful? I clicked on it (and then on Hide Details) but see no difference in the display.
@Ron Newman
I believe that when a TA adds comments, you can see them in-line in iSites.
In later assignments, we may provide some feedback via this mechanism, but not yet. We didn't use iSites for the last two years of the course, so we've forgotten the features.
Thanks. I added a few comments of my own with the submissions -- I assume the TAs will see such comments.
@Ron Newman
Don't count on it. TA's will be optimizing to give a "thumbs up" to students, and will be focusing on what is strictly required by the assignment.