For average home/office use, there's no significant advantage to gigabit - sure a large file transfer might take a few seconds less - but unless you're constantly transferring large files, it's not going to make a heck of a lot of difference.
A couple of years back a friend of mine bought a building to house his small (but rapidly growing) law practice and we wired it CAT5e and because I got a good deal on a 16 port gigabit switch (the equivalent 100mbps switch actually cost a few bucks more), we went gigabit - the servers already had gigabit interfaces as did a few of the desktops.
It didn't make a heck of a lot of difference - practice management applications that take 30~45 seconds to open up, now take noticeably less time, maybe 10~20 seconds - but, since you start the app once a day, there's no significant time saved.
Sure - we can push large files over the LAN faster and run backups in less time, but unless you're constantly moving ginormous files around, you're not likely to save a significant amount of time.