bill - 5:49 am on Mar 5, 2010 (gmt 0)
A 64-bit system can overcome the 4GB RAM limit of a 32-bit system. It is almost pointless to get a 64-bit Windows 7 machine with 4GB or less of RAM. I would say that 8GB might be the minimum you would want to consider.
People don't seem to be reporting any problems but there is a lack of reports since the beginning of 2010.
With your RAM at 8GB it shouldn't be problematic at all for most. If you want to hang on to the machine for a while then packing on as much RAM as you can afford will keep you happy for a while longer.