It is currently impossible to join an Minecraft server with both the server and the client running the version 1.5.2 using the new Minecraft Launcher with a 1.5.2 profile.
The server responds "Failed to Login : Bad Login"
The server has just been created before running Minecraft.
The client is unmodified too.
Edit : This doesn't work in the 1.0.5 version of the Launcher, but seems to be resolved in the 1.0.6 version.