DDR RAM is going up in price generally, as fabrication plants switch to making DDR-2 modules for PC's, WinLaps and perhaps future Macs. There will be a slight shortage of DDR PC3200 modules, particularly in the 1 Gb size through the end of the year at least.
When you get Crucial or whatever RAM from NewBestTigerEggBuyComp.com, you are not getting a guarantee of compatibility with Mac, so you are assuming the risk of shipping cost, time and trouble, not the seller. And the iMac G5 with Tiger is the most picky Mac currently sold vis-a-vis RAM compatibility.
To recap: Apple demands not only that the speed and electrical spec (PC3200 2.5V CL2.5 etc.) are right, but that the Serial Presence Detect settings are correct as well. These don't matter much to most PCs, so the cheapest RAM vendors don't bother checking the settings, 'cause that takes extra time and cost. Good Mac vendors will ensure these SPD settings are right, will test each and every module, and do random tests from each batch in different Mac machines. Discounters and volume online sellers don't, obviously.
Different models of Mac also have different tolerances to marginal RAM. It's not uncommon to see RAM that fails in an iMac or Mini work fine in a PowerMac G5 - this is not because the RAM is good, it's just that the PowerMac has more leeway for error and can run the out of spec RAM. This is a problem when a major OS upgrade like 10.4 or a firmware upgrade comes out, though, because all of a sudden RAM that was out of spec but functioning might stop working - just because the new OS is holding the RAM to standards more rigorously.
Thanks
Trevor
CanadaRAM.com