The meta in the .deb located in the ppa doesn't conflict with mongodb-clients but should..

ecarroll@x200s:/usr/local/bin$ sudo sudo apt-get install mongodb-10gen
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
libboost-filesystem1.46.1 libboost-system1.46.1 mongodb-clients libboost-program-options1.46.1 libidl-common libboost1.46-dev libidl0 libboost-thread1.46.1 mongodb-server liborbit2 libboost-dev
mongodb-dev
Use 'apt-get autoremove' to remove them.
The following NEW packages will be installed:
mongodb-10gen
0 upgraded, 1 newly installed, 0 to remove and 7 not upgraded.
Need to get 0 B/52.0 MB of archives.
After this operation, 126 MB of additional disk space will be used.
(Reading database ... 264254 files and directories currently installed.)
Unpacking mongodb-10gen (from .../mongodb-10gen_2.2.0_amd64.deb) ...
dpkg: error processing /var/cache/apt/archives/mongodb-10gen_2.2.0_amd64.deb (--unpack):
trying to overwrite '/usr/bin/mongoimport', which is also in package mongodb-clients 1:2.0.4-1ubuntu2
dpkg-deb: error: subprocess paste was killed by signal (Broken pipe)
Errors were encountered while processing:
/var/cache/apt/archives/mongodb-10gen_2.2.0_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

If you're going to publish the package as "mongodb-10gen" you should have it conflict with the packages from the canonical repos. Then it'll force remove their packages and all will install fine.