On my list of 25 Before 25, number 23 is "Participate in a photo challenge."
There are many out there, some topical (ie, landscapes, macros, etc), some time constrained (31 days), and some free form.
It's already past the first of the year, so it seems a little belated to do a 365 day challenge (though technically, the 365 days can start at any time). A month long challenge seems more manageable. I'd really like to push myself and do the 365 day challenge, though I don't want to set myself up for failure. Maybe I'll start with 30 days and then if that seems to be clipping along, I'll extend it.
I'll be uploading my photos to Flikr as well as to a separate tab at the top menu bar. Make sure to check back often!