I run a Intel DX58SO motherboard which is limited to 16 GB. A.F.A.I.K. there is no way to place in more memory (http://www.intel.com/support/motherboards/desktop/dx58so/sb/CS-029865.htm
For the moments I still have a number of options* to speed up things, so I am fine.
As long as I buy stuff that I can use later on a new machine there is not to much risk in it. All paart below can be used in a board like the intel dx58og allowing me to go for 48 GB, although it might be better not to make the decision on a new motherboard based on an old one.
-adding an extra PCIE-revodrive to limit the waiting time for the processor (pagefile) and have more space to keep all projects I am working on at SSD instead of having to copy them hence and forth.
-replacing the cheap 128 bit GPU I use by a faster 256 bit version allowing me to speed up the editing
and in the end I could replace the i7 920 by a faster one fom this list (http://processormatch.intel.com/CompDB/SearchResult.aspx?BoardName=DX58SO&Lang=en-US
) but that is not something that is easily taken to a new motherboard in the future.