It really depends on how important it is to you to have a rock-solid system. Personally I find it abhorrent that memory is the ONLY component which manages data on most desktop systems that has NO error checking whatsoever.
I've been stung by very occasional intermittent memory problems in the past, so I elected to go with ECC memory on my new Core i7 system (actually a Xeon W3520, equivalent to a Core i7 920). I chose that because I consider my data to be the most precious thing on my computer system and the thought that it might get scrambled unbeknownst to me is very scary.
If you're JUST using the system for gaming, then rock solid reliability may not be the highest thing on your list of priorities, so ECC may be overkill. But if you also use the system to store important or precious data, then IMHO ECC is a very good idea.