Pros: Clever concept and device. Inexpensive.
Cons: Finding support files is a chore. Firmware upgrade is necessary and laborious.
The bottom line: If you're looking to attach a stand-along hard drive to a network, the Linksys NSLU2 is a good choice.
Today, I received a Linksys NSLU2 Network Storage Link that I bought used on eBay. It was accompanied by a Maxtor 160GB USB external drive. Setting this thing up was one obstacle after another, and the primary purpose of this review is to memorialize the problems and solutions which I suspect most users will encounter under similar circumstances. Following the suggestions in my comments presume some knowledge and experience in installing hardware and software including Zipped and PDF files.

1. The seller did not include the installation CD. Normally this is not a problem since software is usually readily accessible on manufacturer's websites. Not the case with Linksys. You will NOT find a link to the set-up program through either the download page or the NSLU2's product page. You will find the Quick Start and User Manuals there as PDF files. The link is too complex to list here. Just follow the usual path via the "Support" option on the main website http://www.linksys.com The "Quick Start" manual contains sufficient information to get going.

Tech. support responded to my email with the following link to where the set-up utility is actually located: ftp://ftp.linksys.com/pub/network
The file is NSLU2-SetupWizard.zip This Zip archive contains the "SETUPUTILITY.exe" program necessary to configure the device.

2. If purchasing a used device, installation may go easier if you reset to factory default settings. The documentation will then be correct. (The previous owner of my unit had changed the password and IP address to some unknown values, so I couldn't just use that method to log in.) Simply connect to the power supply and insert a bent paper clip in the "Reset" hole on the back of the device.

3. Earlier versions of the firmware will NOT support hard drives formatted for Windows (FAT, NTFS). The earlier devices required hard disks to be formatted using a file system called "EXT2" which is native to Linux. When the NSLU2 is initially set-up with a connected hard drive, the setup utility prompts the user to reformat the hard drive. ALL DATA ON THE HARD DRIVE WILL BE LOST and the hard drive will be re-formatted in Linux/EXT2 file system. If you then plug the hard drive directly into the USB port of a Windows computer, it will not be readable. The hard drive will only be readable by Windows when connected through the NSLU2. However, the latest firmware release (2.3R63 as of October 2006) DOES support FAT/HTFS hard drives, so upgrade is highly recommended. The zip file containing the firmware is accessible through the download or NSLU2 product page on the Linksys.com website. As of October, 2006 the file name for the lastest version is NSLU2_V23R63.zip.

4. I tried upgrading the firmware through the method recommended in the manual: i.e. logging into the administrative panel, Upgrade, etc., but received the message "Upgrade: No [sic] enough free space". Apparently, this is a common problem, since the vendor website has a lengthy (and well-written) procedure to upgrade manually. The link is, again, too complex to post here, but go through the "Support", "Easy Answers", "Network Attached Storage (NAS) Products", NSLU2, NSLU2 sequence; enter "Firmware" in the "Search:" box and it will take you to the procedure. Their "Answer ID" is 2901. The procedure was long, but it went smoothly with no problems and the result worked for me, at least so far.

After about an hour, everything is working properly.

A couple additional points. As reported by other reviews here, the device will not support hard drives greater than 250GB. I have, however, not found an "official" pronouncement. The Firmware Release Notes do not say anything. Also, there seems to be a lot of third-party software written for the device, some of which is listed on the download page at Linksys's website. I haven't looked at it yet. This has been enough aggravation for one day.