Hi, I have been using Ubuntu for about a week now and I'm very impressed with it - seems much more stable and faster than Windoze V*sta.
I have an Iomega 250GB USB drive formatted in NTFS which I regularly use on my XP box at work and my Ubuntu Jackalope laptop at home. But sometimes it fails to start on Ubuntu - I plug it in and nothing happens. Sometimes it mounts just fine.

I always make sure to dismount properly before unplugging (although sometimes XP is very reluctant to let it go, occasionally forcing me to shut right down so I can unplug it - very annoying)

any ideas?

Some laptops don't have quite enough juice to power external USB mass storage drives over the USB connection. This might or might not explain consistencies. If your drive uses external power from an adapter, this won't be an issue.

You should also make sure you're not plugging on a USB hub.

Next time you plug it in and nothing happens, run the dmesg command, or use "dmesg | tail" (to see the end of the dmesg output), to see what the system reports. *Something* is happening, just not what you expect.

And check your USB cable (by trying another one).
If the drive doesn't spin up when you plug it in it's either power (michapma) or a bad cable.
Linux will not see it until it has spun up.