The damage done by Bleed is based on the damage you do, so the stronger you get the more effective it is. Reflect is based on the damage done to you, so the stronger you get the less effective it becomes. It still may be useful (though opponents tend to have a lot more hit points than you do), but personally I avoid that type of skill, since IMO the purpose of building your character is to minimize damage taken and maximize the damage you do.
Larian changed Bleed a bit in DKS, but I found it quite helpful with my warrior in D2:ED (level 10 gave a 32% chance of doubling your damage). In DKS, level 7 gives a 25% chance of doing 23% of the original damage per second, for the next 5 seconds; level 15 gives a 33% chance of doing 47% original damage per second, for the next 4 seconds (so almost tripling the damage).
