All right, slogged through the whole *22* pages. That was a lot of posts, so forgive me if I accidentally repeat a point already made.
People seem to want to compare the benefits of earlier editions' and 4e's multiclassing, as well as one of the costs---feats, I don't believe anyone has mentioned some of the costs that no longer apply. Specifically, when you multiclassed in 3e you paid for it in one or more of to hit, potential hit points and saving throws, as well as the lost class abilities. Obviously, each of those costs was higher for some classes than others, but they were all costs that had to be balanced against benefits. With the 4e system, you keep the standard hit points for your class for a given level, as well as the standard progression for the other numbers. For defenders and strikers in particular, that's a reduction in costs. I don't think that it automatically validates replacing those costs with feats in and of itself, but it needs to be part of the equation.
I also want to go WAY back and mention that, although the rogue's sneak attack can only be used once against a target with the relevant feat, while the ranger multiclass feat's potentially lasts for an entire encounter, the number for sneak attack goes up with level, while the other number appears to remain static at 1d6 (or 1d8 with the appropriate feat). Again, not sure it's equal, but should be considered.