I'm currently using Komperdell C3 Airshock (carbon fiber) poles, 14.5 oz./pr., purchased in Fall 2004. These are made by Komperdell for EMS. I haven't had any problems with slippage as long as I lock them properly, although a twist-to-tighten system always begs the question "how tight is tight?" Before that, I used Masters Kompressor (aluminum) poles c. 2002, 25 oz./pr. (All weights are from my scales and include the small basket and straps.)
I strongly recommend carbon fiber for several reasons: 1) the swing weight (from your arm movement) is much lighter, read: no fatigue after many hours of use (compared to the 25 oz. aluminum poles, but you can get lighter al. poles); 2) there's no clank/clink noises from metal-on-rock (or tree) as the carbon seems to dampen most sound; and 3) no fear of long-term corrosion (although you should still clean the locking mechanism regardless of pole material).
Lesser reasons: the carbon weave is fun to look at in bright sunlight, there's no chance of electrocution when waving off that bear under some low-strung high-tension lines, and, well, carbon fiber is just plain cool. (Besides, CF trekkingpoles are a helluva lot less expensive than a CF bike frame…).
I baby the CF poles when there's any chance of crushing or overbending during transit; however, on the trail I give them all the abuse I can. At 6' and 220 lbs., I can exert a helluva bending moment on the poles, and so far, so good.
I always use poles, even on day hikes, and the CF poles are just easier to take. Plus, with a bum knee I can walk and climb with hardly any knee pain. And although the non-collapsible poles are lighter, I need the collapsible lengths for public transportation. The only improvement I can think of is a practical 4-section collapsible pole, simply to make collapsed length shorter.
Simon

