I selected the defaults in partitioning my drive and df -h shows:

Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
                       18G  2.5G   15G  15% /
/dev/hda1              99M   12M   82M  13% /boot
none                  126M     0  126M   0% /dev/shm

Now I am getting ready to install Scalix CE and it is telling me a whole story about what my partitions should be.  Note that I did the install with 256Mb memory, and I may upgrade to 512Mb.

/ (root) partition of 6Gb recommended.
/boot partition of 75Mb (that seems to be met)
/swap partition of x2 installed memory
/var partition of at least 10Gb (well that is based on a 100 users and 100mb and that is enough for me)

There is also the note:

Some versions of Linux include the Logical Volume Manager (LVM). Scalix Corporation recommends
using a LVM volume for the /var partition. This enables you to increase the size of the
/var partition and back up the Scalix Server without having to shut down the system.

So what do I do? 

leave things alone
Use a partition manager (whcih?) to adjust and create partitions
Reinstall and select manual partitioning