To be more specific, he refers to master/slave replica pairs, which have now (since 1.6) been superseded by arbitrarily sized replica sets. Also, MongoDB now (since 1.8) has single server durability due to a write-ahead journaling protocol. The namespace limit is also a bygone limitation as you can now specify the size of your namespace file. There are probably a lot more things in the post that are no longer relevant, but I haven't used Mongo in awhile.
Additionally, most of what is actually relevant (file handle limits, oplog sizing) is now fully documented in the MongoDB manual.
Yes... it took me a while to realize that this was a very outdated article. (It hit me when I read about background indexing which was supposed to be coming in "1.3".. we're now on 2.2.2.
A mod really ought to append a (2010) to this post title.
