I'm a huge fan of the photo checkin on Foursquare. When I see a friend checkin somewhere interesting to me, I always leave a comment on that checkin saying "photo checkin pls" and I usually get one back.
The checkins with the photos are the ones that stand out in the feed on the phone. And for that reason, I put a photo in almost every checkin I do. It just makes Foursquare so much richer.
But the killer move is the "multi photo checkin". Not everyone knows this but you can add more photos to a checkin. If you just open that checkin on your phone, there is a camera button that allows you to add more photos.
When Christina went down to OccupyWallStreet, she did a twelve photo checkin which I can't seem to find on Foursquare right now or I'd link to it. It's essentially a photo collage of her visit there. It is great. (update: Christina provided this link to her OWS visit in the comments.)
These multi photo checkins remind me of the blog posts Gotham Gal does on her restaurant reviews. In fact Foursquare could make doing a restaurant review on a blog a piece of cake with a slick export checkin feature. Consider that a feature request Alex and Dennis.