First of all, I think the widget looks great. But it had a few problems for us. You can take a peek at how we used it, the campaign widget we used is still up.
We would remove the general donation form from the widget, if we could, and then move the list of fundraisers to that position. The widget was way too long.
We would hide the fundraiser signup button since we don't want anyone to sign up without registering. We had the registration link on top of the page where the article about the swim is displaying now. We had maybe ten participants who didn't bother and went right to this link.
If you go to a swimmers page through the widget on our website, it is not clear you are on the swimmer page because the swimmers customizations and donors fall to the bottom of the page below the list of other fundraisers. Better to leave the other fundraisers off it all together, IMHO, so the fundraiser whose page it is, gets all the attention.
The login link pops open at the top of the widget which is totally hidden in this case so it feels like a dead link. I had participants tell me that they couldn't get back to their page, but I suspect that they missed the login pop-up because it had been hidden from view.