Always report as much information as you can. Too much information is always preferable to too little information. Superfluous information can be filtered out; developers like to play guessing games with code, not with bug reports.
A good bug report should at least include the following information:
Exact version of the operating system (usually output of uname -a).
List of all packages installed on your system (output of pkg_info).
Your environment (output of /usr/bin/env).
If you are building from ports, note approximately how long it has been since you last updated your ports tree. If it has been more than a day, or if you have not run portupgrade -a, do not bother sending a bug report until you have run cvsup and portupgrade.
Information specific for each type of breakage:
If you have a solution or a workaround for the problem, then include it into your report as well, even if you are not quite sure that it is a proper fix. Even if the fix is not quite right, it could still point others in the right direction.
Once you are sure it is a new problem, there are several ways to report a bug in GNOME running on FreeBSD: you could send a report to the freebsd-gnome mailing list, file a problem report in the FreeBSD bug reporting system, send your report to the application's developers via the GNOME bug tracking system, or any combination of those.
If the problem is FreeBSD-specific (usually, this means a problem with building or upgrading), then report to the freebsd-gnome mailing list, or file a bug report through the FreeBSD bug reporting system.
If the problem has to do with an application's behavior, report the problem directly to the application's developers through the GNOME project's bug tracking system
If the problem is quite serious, not necessarily FreeBSD-specific, and you have a fix available, report it to both the FreeBSD GNOME team and the application's developers. This way, the application's developers can apply the patch to CVS, and the FreeBSD GNOME team can apply the patch immediately to the ports tree without needing to wait for the next release.