If you are a developer, create a separate partition and put your home on the root / of that partition, then mount it on the root filesystem.
Benefits:
- you can easily share your home between multiple operating systems: just mount it up, and all your user configs will be automatically reused across multiple development environments.
- if your home HD gets filled with large downloads, your system won't get into trouble, since it uses a separate partition.
An alternative is you have multiple users that you want to backup, is to put each one as:
/user1
/user2
on the partition.
When you boot, make sure to make the directory readable by the user:
sudo mkdir /home/user1
sudo chown user1:user1 /home/user1
On Ubuntu 14.04 Live Install, you can setup a home partition at the "Do something else" installation step: just select the partition and mount it on the right place.
Use the same username on new systems, and mount the partition automatically with fstab. For every new system, just copy the fstab line.
30GiB is a good size for each Ubuntu 14.04 root partition. Leave everything else for the home partition.