Great question, probably one that is running across the mind of anyone who reads this post.
The answer is yes.
There is a usb port at the back of the Seagate GoFlex NET, furthermore I have seen people use different seagate drives on the Seagate GoFlex NET and drives having a different make and model too.
Sometimes even using a SATA cable like this one (That image is not of the GoFlex NET, it is only to show you the cable used). I believe there are many types of cables that can be used to interface with the Seagate Goflex NET connector.
The device has an bracket as well, that can be used to accommodate different drives. Just to give you an idea of the connector, once the USB connector on the Seagate GoFlex Freeagent 1TB is removed it looks like this.
Having said that, to add my personal opinion, I have not personally tried adding any other drives except the Seagate GoFlex Freeagent 1TB drives. The sequence of my purchases was, I bought one of the Seagate GoFlex Freeagent 1TB drives then the Seagate GoFlex NET and then another Seagate GoFlex Freeagent 1TB.
After buying my initial Seagate GoFlex Freeagent 1TB drive, I was so happy with the performance of the drive(in comparison to a drive I won't name here to avoid slandering the product) I decided to get the GoFlex NET and then another Seagate GoFlex Freeagent 1TB, this may sound like I am trying to sell the Seagate GoFlex Freeagent 1TB drives.
However, my thoughts are that if your sticking with a seagate product, stick with it all the way! I have heard of people attaching all kinds of drives to this device, installing Debian on it, running it as a web server or a mail server. Sure, it's cheap and very stable.
I use it at home, for personal downloading. I like a neat setup rather than having cables and wires all over the place. I also like the idea of using the stock firmware(with tweaks), I never have to worry about coming home to a device that is not booting or not connected or something like that. Zero mantainence. I just plug it in, add torrents and then forget about it.
So, Renny, I guess it is what you want to do with the Segate GoFlex NET, if it's something you want to tinker with, troubleshoot and have fun with, if you have the time (bandwidth) to do that, great! I have heard the device accomodates all kinds of drives.
Umm, yeah and btw I heard of people using a USB hub connected to the USB port at the back and then connecting multiple drives.