Originally Posted by froze
aluminum keeps the plastic from cracking.
Not in my case. My rear SKS cracked for no apparent reason after less than a year of use. I don't recall any impacts, sticks, or stresses that would have contributed. It cracked right at the apex, not next to any mounting hardware, and the mounting didn't require bending the fender in any way. I really was surprised by this, since the plastic/alu laminate sounds like it should work great. Maybe mine was an anomaly, or had some defect that I never noticed.
I've replaced it with a Freddy hardcore, which has been on for less than a month. No rattling. I like the round profile and greater width of the Freddy, but it's far too soon to tell if it will be more durable.
As for removing fenders, Sheldon Brown just announced a replacement nut for centerpull brakes that allows you to mount fenders on the back side of the fork, and on the front of the rear brake bridge when using recessed hardware. Look here:
http://sheldonbrown.com/harris/fenders.html. I use older brakes with a through bolt, so haven't needed such a device, but it sounds like just the ticket.
Jack