Depending on your setup and hardware, a remote upgrade is pretty decently
easy. Here I have the privilege of serial console, and then the remote
upgrade is identical to the local one; except of rebooting to bsd.rd
instead of the CDROM.
And then there's yaifo (in ports), which gives you bsd.rd+sshd. You must
get the config correct so it knows the interfaces, but it will be a good
choice for some people. Especially if you'd like to repartition, etc.,
remotely.