Setting the Biome Size in the configuration files to 2 actually does work now, resulting in a small land mass with smaller than normal sized biomes. (This used to be an ignored setting in previous versions.) Unfortunately it seems to be having a direct opposite affect on all of the ocean biomes now. I generated three different maps from three random seeds, each one generated using Biomes O'Plenty (all under MC1.6.2) with Biome Size set to 2. Every single time I would spawn on a small to tiny land mass (sometimes just a tiny island) that would be surrounded by ocean in all directions for a minimum of 100,000 blocks distance from spawn. (I stopped at 100,000 blocks because I got bored after checking that in 8 separate compass point directions several times over.)

On the third map I stopped at +120000, 65, -120000 and saved the map then exited the client. I went into configs, adjusted the biome size back up to 3 (from 2) then reloaded the client and the map at the same position. Once I did this I was able to go a mere 12 chunks north and immediately found a massive land mass stretching off from that point.

This has been fairly consistently testable for me, so it should be reproducible for anyone else.

Same issue, but changing "Biome Size" is not helping in my case.

this will be fixed in minecraft 1.7

Another variation of this I saw was when I disable a bunch of biome you start getting alot more water deposts ranging from swamp depth like lakes, more rivers, and more small oceans. Although a side issue; I wanted to only have semi-flattish biomes so I turned off all the high- or deep evelvation biomes as well as all the cold or "dark" biomes. For me I wish all the biomes could be adjusted by an altitude amplifier (as in 0.0 to 1.0);