You probably wouldnt want to try to use this drive as a primary drive, but as a secondary storage device, 30MB/sec is pretty darned good. With a 120GB capacity, plus the compression that exists in most backup applications, you can save a considerable amount of data to the drive. Another potential application is expandable storage for media files. Why store all those MP3 files on your desktop system? Put them on an external drive, and you can take your music catalog with you.
If you opt to buy an off-the-shelf solution versus building your own, assuming you shop carefully, a 120GB drive plus the enclosure will set you back about $240 for a brand-name external drive manufactured by Maxtor or Western Digital. The Maxtor 5000DV (check prices), which is rated at 1 million hours MTTF, supports FireWire as well as USB 2.0. With the Western Digital, you have to choose between USB 2.0 and FireWire. Finally, both companies offer higher capacity drives -- up to 250GB in Maxtors case.
The fit and finish are often less polished, and assembling the case can be a real chore. Power supplies are often substantially noisier. On the other hand, you can buy them pre-assembled, so that may be a minor issue. If you do-it-yourself, in this particular case (no pun intended), it may be worthwhile to shop around and buy a solution instead. The best pricing for a 120GB 7200rpm drive with a 2MB buffer hovers around $135 . Of course, thats not as much fun. But then, building a secondary storage device may not be your idea of fun anyway.
A host of white box shops will sell you drives in USB 2.0 enclosures -- and in some cases, dual-interface cases -- and only charge around $165-200 for a 120GB drive plus enclosure-- but these enclosures are often not as convenient as the $80 (street) Belkin chassis.