OpalCalc is AWESOME! I registered it a few weeks ago after using the free version for a long time (years?)
Mostly I can only say good things about it. It works the way my brain thinks. I guess the only feature that I'd really like to see is a history/memory of previous calculations. This should only be implemented if you can do it without causing a performance lag, though.
Another "what if" idea I had was to implement a "workday" function. The idea would be to have an .ini file of holiday dates in the program folder. Then you could have a function like in spreadsheets. =WORKDAY() Would be cool. In truth, I probably wouldn't use it often. I would use a history function though
EDIT: I just installed the newest version, and yes, it is faster! I like the new Volcano skin. I think that we can all agree it looks awesome with the Jupiter skin I have going
http://i.imgur.com/7zvzP.jpg <wink>
I'm not sure if the 'Saturation' sliders work as expected though. They seem to change the tint somewhat, rather than "saturation" per se....
(note: The inner colors are the OpalCalc skin and the window border is a WindowBlinds customization based on my wallpaper--which is a pic of Jupiter I scored on Reddit. The extra window border buttons are ActualWindowManager, which I won in a drawing here on DC.)