Interested in learning more about scaling MongoDB? Pick up September’s issue of PHP|Architect magazine, the database issue! I wrote an article on scaling your MongoDB database: how to choose good indexes, help handle load using replication, and set up sharding correctly (it’s not PHP-specific).
If you prefer multimedia, I also did an O’Reilly webcast on scaling MongoDB, which you can watch below:
Unfortunately, I had some weird lag problems throughout and at the end it totally cut my audio, so I didn’t get to all of the questions. I asked the O’Reilly people to send me the unanswered questions, so I’ll post the answers as soon as they do (or you can post it again in the comments below).
Kristina Chodorow's Blog 
hi，kristina, thank you for your webcast, i have a question about objectid, as “A BSON ObjectID is a 12-byte value consisting of a 4-byte timestamps…”, can it someday have some conflits?
LikeLike
When it wraps around in 28 years, it may cause problems. If this becomes imminent, we’ll probably add a new BSON type. If it bothers you, you could come up with your own type, use GUIDs, etc.
LikeLike