How about limiting the number of photos that can be uploaded on a per blog-entry basis? Say 10 or 20 or whatever total photos per blog entry. Then you can get creative and say give 50 more for being a featured blog, or traveller. Or sell more space etc.
Also, how about allowing photos & blog entries to be tagged by lat & long as well as by "nearest place." Sometimes the photos are not from anywhere near anywhere ;)
Some people are starting to geo-code their photos using GPS data to auto-tag the photo with the location, so using lat, long to locate photos on a map would greatly simplify import of geo-coded photos.
Third thought:Great site, like it a lot and I'm sure it will be huge so better start planning for that now!