We started an Ubuntuserver for versioncontrol and would like to access our repositories via ssh.
As we need to give access to several external developers I thought it would be the best way to create a group per project and add the users to it which should use the repository. I cannot say how many projects will be created in the future, so I wonder if we could run into problems later.
Is there a maximum number of existing groups or groups of which a user can be member of in Ubuntu 12.04?
Yes, there are limits. Linux now supports 65536 groups but you will need to use ACLs and RPCSEC_GSS and NFS version 4.0 or higher if you need more than 16 since AUTH_SYS historically has a limit of 16 groups.
Besides the NFS<4.0 limit of 16:
The maximum number of groups is up to 232 starting with version 2.6.0 of the Linux kernel, like the maximum number of users. Still, one user can be a member of at maximum 32 groups on a modern linux.