Standard directories for save data-Win/Linux/Mac?

So for my current game, I need to save game data. I want to save the data in the proper standard locations, and I have a few questions:

Windows
The two places in windows that seem to be the place to store user data are:
[drive]\Users\[username]\Documents\[appname]
[drive]\Documents and Settings\[username]\Documents\[appname]

Which one is the proper one to use that will have the greatest compatibility on all platforms?

Also, how do I detect the proper username/path values from inside BlitzMax?

Linux
From what I understand, the two places to store the data are:
[volume]/etc/[appname]
[volume]/home/[username]/[appname]

The etc directory is where to store info for all users, and the home directory is where to store user-specific information, am I correct? Do many Linux dist deviate from these standards?

And once again, how do I detect the proper username/path info from inside BlitzMax?

Mac
[volume]/Applications/[appname] for application data
[volume]/Users/[username]/[appname] for user specific data

Is this correct? And once again, how do I detect these values from inside BlitzMax?

You can find out all the user document and application paths using Brucey's fantastic cross-platform Bah.Volumes module... I was hoping to see if I could get these added to the official mods, but Brucey hasn't got back to me yet... :-(

...Obviously of no use to anyone...

Wouldn't it be better organised in functions rather than global wobals injected into the code? :D