Unfortunately, there are not many perks involved with being a committer. Recognition as a competent software engineer is probably the only thing that will be of benefit in the long run. However, there are at least some perks:
FreeBSD committers can get a free 4-CD or DVD set at conferences from FreeBSD Mall, Inc.. The sets are no longer available as a subscription due to the high shipment costs to countries outside the USA.
FreeBSD developers may request a cloaked hostmask for their account on the
Freenode IRC network in the form of freebsd/developer/freefall name or freebsd/developer/NickServ name.
To request a cloak, send an email to Eitan Adler <eadler@FreeBSD.org> with your
requested hostmask and NickServ account name.