I want my users to be able to log their weekly progress during an upcoming event we're hosting. A form would work fine, but I'd really like them to be able to see (maybe even edit) their previous postings. A content manager tool like this K2 plugin was suggested to me. Will it fit the bill?

They'll only be submitting two fields: the date and a statistic they are tracking. I'll need to capture their username as well so I can identify their records. They should only see their own records though.

Do you think K2 is the right route for me to try? Or would anyone else have any other options?

K2 is sufficient for submitting the date and statistics, but you will need a hack to restrict the access to their own records, or its better to find another component specific for this purpose.

I've developed an activities logging component before for one of my clients, I can customize it according to your needs, please contact me if you want to get more details.