anyone who really knows filesystems, can you explain this one to me
 

I have two identical drives, both 500GB.

Primary is called "earth" and secondary is called "backup"

In terminal:
$cd /Volumes/
drwxrwxrwt@ 5 root admin 170 Nov 21 16:34:28 2007 .
drwxrwxr-t@ 33 root admin 1190 Nov 21 16:32:29 2007 ..
drwxrwxr-x 10 me staff 408 Nov 21 16:35:15 2007 backup
lrwxr-xr-x 1 root admin 1 Nov 21 16:32:12 2007 earth -> /
drwxrwxr-t 8 root admin 340 Nov 21 16:34:30 2007 earth 1

As you can see, there are two listings for earth, "earth", and "earth 1". Most apps do not show a distinction, like Disk Utility does not see three drives. However, Activity Monitor in the disk area, shows "earth" listed twice. There is no numeral 1 after the name.

Now, in terminal, if I run `open /Volumes` a Finder window opens with three aliases in it:
backup
earth
earth 1

Each shows different contents:
"earth":
Applications
Library
System
Users

"earth 1"
Applications
dev
home
Library

Anyone have any idea what is going on? As a side note, I just pulled the "backup" drive out, to replace it, as it was making some strange noises, and while that drive was not initialized, the above issue was not there.

I am running 10.5 and did not notice this issue on 10.4, though I may not have looked for it.

Looks to me like the "earth" volume, which you're currently running from, had been the target of a copy operation in the past that might have failed, and that "earth 1" is its old mount point, now converted to a folder...

Got any suggestions on what to do about it? What's strange, if I go into the Applications folder in either, the contents are identical.

I'd probably remove "earth 1" after making certain that it's not your startup disk (which I don't believe it is) by dragging a file into Applications and making certain it doesn't show up in the "other one".

They are clearly two separate areas:
$touch /Volumes/earth/Applications/1a
$touch /Volumes/earth\ 1/Applications/1b

$ls -la /Volumes/earth/Applications/
total 32
drwxr-xr-x@ 3 me staff 102 Nov 11 2010 Applications
-rw-r--r-- 1 me admin 0 Nov 21 17:04 1a

$ls -la /Volumes/earth\ 1/Applications/
total 32
drwxr-xr-x@ 3 me staff 102 Nov 11 2010 Applications
-rw-r--r-- 1 me admin 0 Nov 21 17:04 1b

What I dont get is why they are identical at this point. I have been installing apps and setting up 10.5 for a few days now, Just today I installed a new app, and it now lives in both locations. I have not tried, nor do I have the ability to restore any files.

I can't retrace your steps as effectively as you can, so I don't know.