Want other people to view your photos? Then you need to get your photo to fall into one of the following categories:
Jacked up saturation. Because the colors of the real-world aren’t as interesting. Link.
Black and white. Because the colors of the real-world aren’t as interesting. Link.
HDR. See also jacked up saturation. Link.
Sunrises and sunsets. Link. (The linked-to photo also contains children, which is another common front-page genre.)
Young women. Even if the photo isn’t very good. If the photographer is a young woman, she can excel at this category just by taking self-portraits. Link.
Bokeh shots. Because it shows off the fact that you have a DSLR and a fast lens? Link.
Ultra-wide angle shots. Shows off that you have an expensive lens? Link.
Cute animals. Because they are so CUTE. Link. This is easier if your own pet is photogenic. Link.
Flowers. Because it’s easier to get a flower to cooperate with you than a cute animal. See also bokeh shots. See also jacked up saturation. Link.
Multiple categories. The more the better. The following photo combines the pretty young woman category with the black and white category: link. The following photo combines ultra-wide angel, HDR, and sunrise/sunset: link (as well as long exposure pictures of moving water, another common front-page genre).
Genuinely interesting shots that don’t rely on one of the above gimmicks. Now this is really tough. You should try to avoid this category, they rarely make it to the front page, and require lots of work. The following shot seems gimmick-free, and made it to the most-interesting lineup, even though I don’t quite think it’s that great, and pictures of doors are still sort of cliche: link.
UPDATE
I should have mentioned two additional common categories:
Postcard-pretty landscapes. Link. Though to maximize the prettiness of the landscape, you want to jack up the saturation, and shoot at sunrise/sunset.
Pictures of food and eating utensils. See also bokeh shots. This is a surprisingly common category. Link.
In the only comment left to the post so far, the commenter suggests that my post is sour grapes. But in fact, I did once have a photo show up on the Flickr most-interesting list of the day. It was my cute animal shot:
You will also note that the photo has bokeh, and I shamelessly jacked up the saturation a bit. The perfect formula to get your photo appreciated on Flickr!

Hi Mike, this all sounds a little frustrated and reductionist. Have you ever thot 'bout the possibilty that the authors (I'm one of them) of the exhibits trotted out to prove your case, have a style that's favoured by the Flickr population and/or the piece of software that's called Xplore and ain't out their just to please and get attention? Probably not.
Regards from Rotterdam,
AZ
Posted by: AurelioZen | March 31, 2008 at 05:13 AM
The downside of getting your image into Explore is that you get a lot of fancy awards in your comments section, I am sure you have seen them.
I don't know if you have looked at this:
http://bighugelabs.com/flickr/faq.php?section=scout
and
http://bighugelabs.com/blog/explore-video/
It might shed some light at this feature.
thanks for the tests you have done to determine the sweet spot of the G-9
...\5-points
Posted by: Peter Szawlowski | April 15, 2008 at 05:32 PM