On a related topic, someone said that she used a mix for her water that provides protein as well as electrolytes and carbs.
I think this might have been my post, and I was indeed talking about Perpetuem. However AFAIK it does *not* include electrolytes...the 3rd component is lipids. (Incidentally, if you decide to try it, be aware that you need to either drink it the same day you prepare it, or else refrigerate it if you mix it in advance - the lipid content means it will go rancid if you just leave it out. I learned this the hard way!)

At first I was bummed that they didn't include electrolytes in the mix, but it makes sense now - when I'm doing long training rides in colder weather I don't want/need the electrolytes though I do need the carbs. If I drink electrolyte-heavy stuff when I'm not actually sweating much, it just makes me have to pee. For riding in hotter weather I'll take along some endurolyte capsules and then I'm all set.

I've been happy enough with Perpetuem that I haven't tried Sustained Energy yet...but here's some comparison info from Hammer's website:

Comparing Sustained Energy and Perpetuem
•Sustained Energy is neutrally (a.k.a. "plain") flavored. Perpetuem is available in three options: an orange-vanilla "Dreamsicle" flavor, a caffeinated caffe latte flavor (12.5 mg of caffeine per scoop), and in an unflavored/plain version.
•Perpetuem contains lyso-lecithin fat, whereas Sustained Energy does not.
•Perpetuem contains tribasic sodium phosphate, which is a tremendous lactic acid buffer. Sustained Energy does not contain this nutrient.
•Both fuels contain l-carnosine (an antioxidant that also buffers lactic acid), l-carnitine (to promote fatty acid utilization), and chromium polynicotinate (to stabilize blood sugar levels).
Bottom line: With Sustained Energy and Perpetuem, you have two great long distance fuel choices. When exercise goes beyond about two hours, you can use either product as your primary or sole fuel, in any combination with each other or any other Hammer Nutrition fuel.

That said, we have noted that Sustained Energy may be the ideal fuel choice when endurance exercise intensity is at a higher level (approximately 70-85% MHR), whereas Perpetuem may be a more attractive choice the longer the athlete goes and when exercise intensity is at a more aerobic pace (under 70% MHR). Additionally, over the years we have noted that Sustained Energy may be the ideal choice for very lean athletes (the "high metabolizer/hyper-metabolic" types), while Perpetuem - with its added healthy fat component - may be the ideal choice for athletes with a naturally higher body fat percentage. The rationale for this suggestion is that athletes with a higher body fat percentage have a greater volume of calories available from body fat stores, which the lyso-lecithin component of Perpetuem may effectively assist in accessing for use as energy.

Again though, because the applications for Sustained Energy and Perpetuem are identical, either fuel can be used as the primary-to-sole fuel during prolonged bouts of exercise. Test each product in your long-duration workouts, under a variety of conditions, to find which product works best for you!
Hm....guess I'll stick with Perpetuem based on that "naturally higher body fat percentage" that I have.