Using mac the issue is a bit different. it spin down and go to sleep within 1 minute. then it takes about 20 seconds to wake up.
Watching a movie that way is a pain.
My workaround is keeping the drive working every 5 seconds while the watching a movie (detect if a movie is playing done by watching the cpu usage.) 
The script I use in a comment of a blog:
http://saffi-stuff.blogspot.com/2008/09/fixing-segate-powersave.html

Did Seagate even make the controller chipset? Seems more like the problem would lie with the manufacturer of the chipset rather than the drive itself. My two cents.

I agree completely with KD. If the power-saving protocol was made open_to_public, would Western_Digital (etc.) really profit at the expense of Seagate's R&D? Or are they concerned that they will have to layoff their device-driver development team as a result of fully-functional free software alternative(s)? What other reason is there for keeping the protocol proprietary? ... Another blatant example of competition_in_big-business and bottom-line_obsession hindering progress. I can only hope that more businesses will follow the new AMD/ATI model.

The article states that the problem doesn't exist on the OneTouch 4. Oh yes it does. I have exactly this problem on my OneTouch 4, bought three weeks ago. The drives goes into sleep mode with a slowly pulsating light. I get "Device not ready" errors in my system log when I try to use it after that. The drive goes into read-only mode, folders and files disappear, etc. I haven't tried the proposed solution yet, but am about to...

http://ubuntuforums.org/showthread.php?t=494673

Since I did this, I haven't had any problems, I'm guessing there's similar solutions for non debian based distros

I would like to express my heartfelt gratitude to Seagate for making it VERY clear what they think of Linux users, and I would like to make it very clear that I will never again buy a Seagate or Maxtor product.

I was about to buy a new SATA drive for the desktop, and Seagate were top of my list until now. Too bad.

"Open the Seagate FreeAgent Tools application. Click Utilities in the Command panel..."

WTF?! This is something that has to be controlled by the OS. I have several external drives that I assembled myself that Linux succesfully puts to sleep when idle for some time. And more importantly - knows how to wake them up again. Same for Mac OS X. Why can't this be left to Windows too?

if you're a competent linux user, you could just set up a script to 'sync' every so often to keep the drive from going to sleep in the first place.

The Linux community doesn't want a workaround that disables the power saving mode. Why should we accept reduced functionality? Seagate should simply disclose enough of the protocol for controlling the power saving mode (and any other interface details needed to make effective use of the power saving mode) so that the Linux community can update its disk drivers to make proper use of the power saving mode. I've been in contact with Seagate customer support over the issue. They are hiding behind the typical "we don't support Linux" claims. We don't demand that they support Linux. Only that they properly document the interfaces to their devices so that the Linux community can support the devices themselves. I don't understand why they are so reluctant to disclose the programming interface.

Hello Nick, 

Thank you for including Seagate's response to your article. I would emphasize that there are no difficulties writing and reading to either a Seagate FreeAgent or a Maxtor. The power management can be turned off. What I sent over yesterday were directions on how to change the settings using a Windows system. Pasted below are Linux directions. 

How to disable power management on FreeAgent drives on Linux system.

1 - It is assumed in this example that the drive is attached to device /dev/sdc

2 - Check that the right drive is selected:
$ sudo sdparm -a /dev/sdc
/dev/sde: Seagate FreeAgent Pro 400A
Power condition mode page:
IDLE 0 [cha: n, def: 0, sav: 0]
STANDBY 1 [cha: y, def: 1, sav: 1]
ICT 0 [cha: n, def: 0, sav: 0]
SCT 9000 [cha: y, def:9000, sav:9000]

3 - Force restart the drive ( if the drive was in stanby mode):
$ sudo sdparm --command=start /dev/sdc

4 - Disable power management:
$ sudo sdparm --clear STANDBY -6 /dev/sdc

5 - Check the drive power management has been disabled:
$ sudo sdparm -a /dev/sdc
/dev/sde: Seagate FreeAgent Pro 400A
Power condition mode page:
IDLE 0 [cha: n, def: 0, sav: 0]
STANDBY 0 [cha: n, def: 1, sav: 0]
ICT 0 [cha: n, def: 0, sav: 0]
SCT 0 [cha: n, def:9000, sav: 0]