I have one of the earlier WRT54G units (before they started dropping the RAM size and eventually coming out with the separate GL version).

Mine just started becoming flaky one day and more noticably with my wife's Dell Windows 7 machine (which also had 802.11n). My older XP laptop at the time didn't seem to care (802.11a/b/g) so much. I didn't investigate much and ended up simply replacing it with a proper 802.11n unit. I do still run it for one device I have that will not properly work as 802.11n since I force the new router to be n only.

Not sure that really helps you all that much though.