Hi Nick
I switched to Eggbeaters earlier this year after a long and happy relationship with Look pedals. My main reason for switching was the price - I could get the EBs for £50 when a decent Look pedal replacement was going to cost me £70 (Keos weren't available at this point). I'm mostly happy with them but do have one reservation which may not apply in your case.
I'm a roadie, which meant that I immediately had to place an order for some road cleats. At £16, these almost wiped out the savings I made by opting for the EBs but they are worth it as they have rubber pontoons which protect the cleats from the floor (and vice versa). They also obviate the need for Kleat Kovers which, incidentally, aren't compatible with the new Keo cleats (a major strike against Keos for commuters).
Compared to Look cleats, the EB cleats cover a smaller area. This is an advantage when wearing overshoes, the undersides of which are prone to getting caught under the edges of Look cleats.
As for 4-sided entry, this hasn't been that huge a benefit for me. I often find it a hit and miss affair to engage the cleat with any of the sides of the pedal, since the hit surface is that much smaller than my old Looks. Having said that, you can slide the foot in either direction to engage the cleat, compared to Looks which can be entered from one angle only.
Compared to the plastic Look cleats, the brass EB cleats are lasting much longer.
To my mind, the only downside of the EBs is the arrangement of bearings. Instead of a set of bearings on each end of the axle (as with Looks), the EBs use a catridge bearing on the outside and a bushing on the inside. One thing I've heard about bushings is that they don't like getting dried out; indeed, I've noticed squeaking noises emanating from the EBs from time to time. I reckon I should be squirting grease into these things occasionally but don't have the knowledge (or the grease gun) to do this.
I also note that there is some lateral play in each pedal. Whether this is due to the bushings becoming worn or whether it's a design feature, I don't know.
Crank Bros sell pedal kits which include a complete set of replacement bushngs, bearings, seals and endcaps. Theoretically, the pedals should last a lifetime (I've never heard of bent axles before now, though) with regular maintenance. You can also buy replacement axles to upgrade a set of ChroMo (say) EBs to Ti ones (say).
Some high-end road shoes only offer a 3-hole cleat pattern. Crank Bros cleats all use a 2-hole SPD pattern; a 3-hole adapter is available but I wouldn't feel right about mounting these things on my expensive carbon-soled booties. If I were rich and fit enough to justify such bling, I'd almost certainly opt for Keos.
Oh, and one more thing: Crank Bros sell a roadie equivalent to the Candy called the Quattro. Like the Candy, it surrounds the EB cage with a platform, which adds a certain amount of weight and puts some weenies off. But the quattro is designed for tighter cornering than the EB and is the better choice for crit racers.
That's it: all I know about Eggbeaters. In conclusion, I'd buy them again for commuting and I wouldn't buy anything else for x-country or cyclocross. For road racing, I'd probably opt for Keos over Quattros (but it's a very, very close call).
Cheers,
Paul