Apparently, a while back, Magnum Research decided that there was a feed issue with the 50 Action Express magazines. Specifically, the last round was leaving the bolt locked open before firing, not after, requiring the user to hit the slide release before the round goes into battery. I've encountered that with my own Desert Eagle, both before and after their fix. But, the parts come in for free, so there's nothing to lose in getting the replacement parts.
Magnum Research decided that it was an issue with the magazine followers they were using on the mags. The old followers had a slot in the center, presumably to help seat the rounds more reliably. The new followers are flat, just like the followers for their 44 magnum magazines. If you are using the old slotted follower, then you're entitled to a replacement follower. I'm not sure whether you get only one per Desert Eagle, or one per magazine affected.
I sent an email to firstname.lastname@example.org when I heard about the follower replacements. MR asked for my Desert Eagle's serial number to confirm, and my replacement mag follower was in the mail shortly thereafter.
The replacement is a fairly straightforward procedure - just remove the floorplate, take out the spring, take out the old follower, and insert the new one.
-- SeanNewton - 05 Apr 2006