Yeah - what SiHa said about task killers is right... often cause more battery drain by shutting down apps that then restart anyway. Android (from 2.1 upwards) is pretty good at dealing with shutting down unneeded apps as and when.
24hrs is not that bad to be honest... I get about that out of mine... I guess I could get a bit more if I wanted, but the way I see it is that I charge it when I'm at home anyway (just plug it in on a night) and I have a USB cable at work (for if I'm running low). There are some who have been getting 2-2.5 days out of their DHD... albeit with not so much use... so it is good to know that, should I need to, I too can get ages out of my phone, but as I said... I generally charge over night anyway!
EDIT - I actually plug in on a night, which is before it gets to telling me that it is running low, unless I have been playing games/surfing the web)
Are you on the stock ROM? One of the benefits of rooting your phone is that you can run custom ROM's, which have been tweaked to improve battery life (I think the people I mentioned that have been getting a couple of days out of their DHD's have been running LeeDroid).
I understand your frustrations though... my wife has a Galaxy S and the battery life appears to be quite a bit better, or at least it was until I rooted (I am on CyanogenMod 7 now)... her's is still better, but not massively now!