I have had system panel on both my Dinc and now my X. My X has had TERRIBLE battery life since I bought it a couple weeks back - something like 4 to 5 hours if I am actually using it. So I decided to try ATK. So far, it has probably quadrupled my battery life. I have it on autokill, aggressive, when screen turned off. Have set to ignore main apps/widgets (browser, messaging, etc). So far I must say I am very happy with the results.
A sidenote - even with ATK running, my phone still was NEVER sleeping. However, the battery life is still very improved. Last night I figured out it is the GPS keeping the phone from sleeping. So I will now keep GPS toggled on/off as the bug reported is indeed true with my X. I expect even better battery life to ensue.