well you seem to have found the main differences although i have one correction for you.
-DDR2 800 max memory support as far as I know, have some issues in memory controller and ddr2 800
that is backwards. DDR2-800 has been found to be the most compatable.
really i can't tell you what to do, it seems you have the main facts needed to make a decision. you have s939 which is well proven, especially in terms of the motheboards available, however will have no
future processor upgrades. then you have AM2, the downside of which would be finding a proven motherboard (in my opinion). in my opinion the glitches in the memory controller are really only a minor issue as i would be buying AM2 only for its future upgradeability, an upgraded processor should have a revised memory controller with these bugs ironed out. from what i hear the problems can be avoided by using DDR2-800. overall in my opinion AM2 is probably the better choice if you think you would prefer to upgrade the processor in future rather than the whole computer. if you think you can upgrade the whole pc i would get s939 for now