i've never had much mud issues with my dx's. mind you i'm a pussy and don't go on muddy trail rides all that often. wouldn't want to get my bike dirty or andything.
i'm use to spd's so i'd imagine egg beaters would take some getting use to. i personally like the fact that spd's have much less float. you still get enough to avoid knee problems, and be comfortable etc. but when you wan't to get out, you can, and with ease. plus it is easier to tell when you've become unclipped. i haven't actually tried egg beaters but i find the idea of have a large degree of float unerving.
on the flip-side my cousins boyfriend went form spd's to egg-beaters and loves them! plus those crank bro's look sexable.
i'm sure which ever you choose tankass, they will keep whatever bike you choose to put them on just as PIMP!
btw which bike will they go on tankass? my money is on the msisle.