I'm new to android, just spent some time searching for answers, found solution and wanted to share my findings;
I have a new Samsung Skyrocket. First time I plugged it into Windows and Mac the drives appeared and I was able to begin copying music. Days later I couldn't get this to work and it took me numerous hours to resolve.
I saw posts referring to a procedure like this; connect phone to usb port, option to use usb storage appears on phone, hit ok, and you're good to go.
This doesn't happen on my version of gingerbread. I have to go into the the usb utilities, choose to use usb mass storage, then it tells me to connect to usb port on computer, I do so then phone says to click ok to continue and if it's successful then phone screen says USB storage in use. That's how it goes when it works. I had this work on Windows and Mac. Drives appeared in file browsers of both OSs.
Now what happened for the past 2 days is that I'd connect phone usb cable computer (and get a notification chirp) but I wouldn't get that succeeding screen on the phone saying ok to continue. Instead it went back to the original usb utility. I jacked around with this on and off for two days, trying, searching for clues.
I also tried connected to a linux box since that's where I really wanted to connect anyway - directly to my music host. Same thing occurred on the phone which connecting to linux (FC14). Odd thing was that I was at first not getting any output in dmesg at all. No indication of any usb device being connected. Weird. Much searching. Nothing.
I ran across some posts about Kies. Looked at that app - it's for copying over wifi. Don't want that. Then I read something about how a guys phone was set with the usb attached to Kies and he had to unattach it. I couldn't find a way to do that exactly so I just rebooted and things started to get good.
Now when I connected to linux I was getting the appropriate usb device messages in dmesg. But I still could not mount the devs. fdisk even failed to display any info at all. Weird. Then I realized I need to go into the usb utils and enable usb mass storage use. Did that and all is well.
Now when I connect phone usb to computer (win, mac, linux) it's mounting and the world is right again.