I know that the way most people partition hard drives now is by making a 
partition for swap and one for /, and that might be all they do.  That is 
convenient in some ways because when a directory needs more space, it can 
access it, if it exists.  On the other hand, with more partitions, a 
directory can only grow to the size of the partition, so partitions limit 
the growth of directories.

Of course, limiting the growth of directories is often a good thing. 
Without partition boundaries constraining growth, if a log file in /var is 
growing at a rate of 1 MB/sec, it won't take long for it to fill up all of 
the free space on the entire hard drive, and when that happens it may 
bring down the system.  So maybe I should use a /var partition to prevent 
excessive log growth from shutting down the system, but I don't know what 
is an appropriate size for /var?  It looks like my current /var is only 
using about 1 GB, but HDD space is cheap enough that I could give it 10 GB 
and not feel like I'm missing anything.  What would you recommend?

I'll want to put most of my space into /home, but how much do you think I 
should leave for /?  On my current system, / (after excluding both /var 
and /home) is only using about 54 GB, and it seems to have a lot of extra 
programs in it that I wouldn't use in the future, so I think 100 GB should 
be enough.  What do you think?  Is 100 GB for / good enough?

If I used 10 GB for /var and 100 GB for /, that would leave about 2.6 TB 
for /home.  These 3TB drives seem to be the cheapest option, per byte, 
right now, so I expect a lot of you will have them soon, if you don't 
already.

Mike