I have to respectfully disagree. Your comment is a bit sweeping and I really don't think that MongoDB's sharding solution is a bad one ... simply the strategies are different.

There is a large set of nice features that makes Mongo, for most people, nice to use long before you even need to address sharding. The percentage of people that will need to shard is much lower than the percentage of people that can get considerable benefits of how you can query data in MongoDB, for example, vs. Riak.

You are such a Riak-lover. :P