As with any emergent technology, it's worth evaluating whether USB 3.0's advantages are significant for you, so first let's take a look at potential rivals. The oldest of these is FireWire, also known as IEEE 1394. In its most common form (FireWire 800) this is a fully duplex interface with up to twice the (practical rather than theoretical) throughput of USB 2.0. Unfortunately it has failed to reach adequate market penetration for it to become the major player. Though most PCs do offer it, it's found on only a minority of laptops and is relegated to a fast-shrinking niche of storage, audio and camcorder devices. FireWire S3200, which should be available towards the end of the year, should offer speeds up to 3.2Gb/s and is completely backwards compatible. This might result in FireWire returning to the spotlight.
Largely responsible for FireWire's decline on the storage front is eSATA. As you might already know, SATA is the connection standard used for most internal drives in a computer, including hard disks and optical drives. eSATA is a version of SATA specifically geared towards hooking up external storage. It is found on nearly all motherboards and quite a few laptops, especially more expensive models.
Though eSATA is not (yet) as fast as the latest internal SATA 6Gb/s iteration, it should give you roughly the same speeds on a hard drive as installing it in your PC or laptop, thus matching USB 3.0 for performance. However, it's also not without its disadvantages. Most netbooks and budget laptops don't support it, cables can only be a maximum of 2m in length and are often difficult to find at anything longer than 1m, and unless you're lucky enough to own a source device using the newer eSATA-P or eSATAP (powered eSATA), you'll still need an external power source.
With longer cables, more possible connections (up to 127 using hubs), superior theoretical bandwidth, far more flexibility (including backwards compatibility at the source end) and more universal appeal, USB 3.0 is well-positioned to do to eSATA what USB 2.0 did to FireWire. Until the next eSATA standard arrives (which will presumably up bandwidth to match SATA's latest 6GB/s and have powered connectors as standard), USB 3.0 looks like the better bet.
So is it for you now? If you're into external storage, we've already answered that question. Whether hooking up hard drives, SSDs or memory sticks, USB 3.0 makes a big difference in real world speed and you'll notice the benefits straight away, and be happy with the investment for the foreseeable future. The other area where USB 3.0 currently makes a difference is high definition webcams, which need the faster connection to enable streaming their feeds through to your computer without the compression that was necessary with USB 2.0 (though how usable these are for video calls will obviously still depend on your broadband speed).
There's also plenty of future potential for Superspeed USB. It could power many devices that previously required separate power adapters, including speakers and monitors. Full duplex communication should also allow more complex interactions between connected devices. Perhaps the most potential is in the likes of DisplayLink, which allows you to run monitors and peripherals from just a single USB port; USB 3.0 will allow clever devices like the VillageTronic ViBook+ and Toshiba Dynadock U10 to really come into their own.
So why might you not want it just yet? If you only use your computer for basic tasks like email, web-browsing, light gaming and office productivity, USB 3.0 probably isn't going to be high on your priority list. It is unlikely to make any difference to your average peripheral, and won't affect your standard definition webcam, mouse, keyboard or printer. Even disregarding limited availability, its inclusion carries a premium, as motherboards still require a dedicated third-party controller chip to make it work. USB 3.0 cables and hubs are also significantly more expensive, with the former likely to be a shorter length than USB 2.0's five metres and the latter limited to a maximum of four ports due to early controller limitations. As such, you may want to hold off until SuperSpeed USB replaces its predecessor as the de-facto connectivity standard before making the transition.