Something I do in the event of OOM problems is run top on the machine
when everything is running normally.

Once it is running you can type 'M' to sort the list by memory usage,
then track down the processes that are using the most memory to find out
which packages they belong to and whether they are things you actually
intend for your system to be doing.

This process would be how I ended up ditching Gnome and KDE...

-- 
Dan