I can't figure out how to put up a pic as my avatar? The generic "blockhead" is actually appropriate! My name is Jeff Block and have a lifetime of being called "blockhead".
"Settings" in the avatar menu (top right), then click on "Profile" in the menu bar. This should bring up a page with the default avatar picture. When you hover over the picture, a small blue "Edit" box should appear near the top right of the image. Clicking on the image should open a local file dialog to upload your image. If this does not work, try with a different browser if possible.
Yep, i find the "only my email address" thing confusing as well - point is, this is only the first in what is supposed to look like a series of tabs - you must click on the "Profile" option in the menu bar above the email address.
If you click on settings, you'll be taken to your profile menu (notice neither Shop nor Make + Sell are selected) from there click on the menu Profile. You should be able to edit your avatar from there.
If something basic like uploading a picture doesn't work here with two major browsers (Microsoft's Internet Explorer and Apple's Safari) then this is not a "known browser bug" but it becomes a Shapeways bug.