...USB 3 itself is not useless, but USB 3.0 headers are. First, the benefit of having a USB header is that you can quickly swap devices through it... Besides HDDs, there aren't likely to be many [other USB 3.0 devices] for a few years...
Second, the benfit of USB 3 is the faster speeds is only really useful in some cases. Such as you're in the habit of copying a lot of large files at once. If this is the case, you'd have a reason to have a USB 3 external HDD, but it's unlikely you would be needing to swap it quickly. In this case, you'd need USB 3, but not necessarily on a header.
Finally, if you do copy large files regularly, there are better ways to do it than USB devices. You'd prbably want to be using eSATA or firewire instead. These will be faster, though less common on consumer external devices. These ports as headers are much more common than USB 3 headers.
So basically, in my opinion, until they start making 1 TB iPods and iPads, having USB 3 headers isn't going to be that useful./quotemsg]
It truly is fun to see how different we all are. Judging by the graphics cards they choose and comments like above, it seems many of the build-it-yourselfers here are gamers. I don't game at all (though I might start with my next mega build). I'm a video professional — camera, primarily, not even a full-time editor — and I currently own 7 TB of data. Once I have my next build in place (I'm thinking i7-2600k and the ASUS P8P67 Deluxe) I project that 7 TB will quickly grow to 12 TB in the next year, easily!
My current system (a 4 year old laptop) doesn't have ANY USB 3.0 connections (obviously). But I purchased my first 2 TB USB 3.0 drive in March. I plan to phase out my 1TB USB 2.0 HDDs and replace all of them with 2TB USB 3.0 drives, while adding a few more. Why USB 3.0 and not Firewire or eSATA? A camcorder is typically filling my Firewire spot. Some kind of Media card reader, is typically filling my eSATA connection. Plus, hard drives are more expensive with Firewire or eSATA.
Under the new system, I would likely have my two most commonly accessed hard drives occupying the back USB 3.0 ports. All of my hard drives currently sit powered and ready to go, just behind my monitor. I have a snake pit of cable ends sitting near the USB ports, all of them labeled (Drives F, G, M, T, U, V, W and X) ready to be plugged in whenever I need them. While some simple edits of Standard-Definition footage can be edited directly from the USB 2.0 drives. It's less than ideal and doesn't work at all for most of my HD formats. So when I need to edit a client's job that was shot in HD, I copy all of the footage (10GB for a small vignette up to 300GB or more for longer pieces). I usually have to start that footage copying the night before an edit. with USB 2.0 we're talking 3 - 4 hours to copy.
I keep most of my client footage for a few weeks to a few months — for their offsite backup as well as for my peace of mind from clients who will almost certainly call and ask me for it, not 5 minutes after I've deleted it. Some footage is kept as backup indefinitely.
In addition to this, I keep regular system backups on a backup drive (which is only connected to the computer when performing my weekly back up). And still other hard drives need to be introduced to create redundancy every drive I currently have.
Yes, I swap drives constantly, while requiring my current working files to be on my internal SATA hard drives. You can see why I don't want to be digging around in the back of my computer to find the only two USB 3.0 connectors all of the time. I cannot tell you how excited I am to ditch my USB 2.0 HDDs. I, for one, cannot get enough USB 3.0 headers!