MySQL gem vs RoR default library

I have Rails v 2.0.2
Ruby v 1.8.6
MySQL db v 5.x

I am confused as to whether we should use the MySQL gem or the RoR
default MySQL support library.
The consultants that had worked on the initial phase of the project
had me remove the gem saying that
it is better to use the RoR library, that the gem was necessary in
earlier version of Rails.
BUT, I get the WARNING below which says the opposite.

Can somebody assert that given the versions of Rails and Ruby I should
be using the MySQL gem or NOT?

I have Rails v 2.0.2
Ruby v 1.8.6
MySQL db v 5.x

I am confused as to whether we should use the MySQL gem or the RoR
default MySQL support library.
The consultants that had worked on the initial phase of the project
had me remove the gem saying that
it is better to use the RoR library, that the gem was necessary in
earlier version of Rails.
BUT, I get the WARNING below which says the opposite.

Can somebody assert that given the versions of Rails and Ruby I should
be using the MySQL gem or NOT?

------
WARNING: You’re using the Ruby-based MySQL library that ships with
Rails. This library is not suited for production. Please install the C-
based MySQL library instead (gem install mysql). SQL (0.003382)
------

In my experience the gem is quite a bit faster...

-philip