I like the alarm...well, I don't like it, but I always want to know when things aren't what I expect. I agree with Ray though, set it up so that you are notified in other ways instead of or in addition to the audible alarm. That's one reason I'm building my own web system to monitor the aquacontroller; I don't always check my email frequently during the day but I'm nearly always available via instant messaging or sms, so as soon as a parameter goes far enough out of whack, I am actively notified.
I would agree, never use the "If Time > 00:00 Then HET ON"...but I thought it executed each line of code independently...so if that was the first line of code and you had other lines turning it off later in the program it would end up in the off position. I could definitely be wrong about that though -- it has been a while since I looked at the manual. Either way, I can't think of any reason you'd ever want that line in there.
I have seen similar lines to make sure pumps or things of that nature are in an 'always on' mode or for a refugium light or something but never for heaters.
In terms of the failsafe code I referenced...it generally looks something like this:
If Temp < 60.0 Then HET1 OFF
(turn my heaters off when the temp probe fails so I don't cook my tank)
If Temp < 60.0 Then LT1 OFF
(turn my lights off when the temp probe fails...)
It really depends on your situation though. The question is, what would you want your system to do if the temp probe wasn't accurate? Would you turn things on...or off? I think the behavior might change based on whether it was winter/summer... The more I think about it, the less valuable I actually think this is, except for certain unlikely circumstances. I might even take my failsafe lines out to simplify the programming.
What I wanted to know is when there was a probe failure. I believe any drastic/fast change in any parameter generally means a probe failure of some sort...and in that case, I'd want to keep things set the way they were prior to the failure. I don't think the AC3 can do that with its built in system. That's the other reason I'm building my own web system to monitor and control the AC3.
I think the advice to keep it as simple as possible is a very, very good rule. Too easy to introduce unintended consequences.