It's nice to be future proof — and USB 3.0 is just one of those things that will soon be ubiquitous — even across hard drives and accessories that connect via USB. While there are definite speed improvements, you should know that USB 3.0 only works when both the host (laptop) and the accessory (hard drive etc.) are USB 3.0 ready.
If you plug in a USB 3.0 hard drive into a USB 2.0 port, it just functions as a regular USB 2.0 drive.
On paper, USB 3.0 is capable of a transfer speed of 5Gbps (gigabits per second) — roughly 10 times faster than the 480Mbps (megabits per second) speed offered by USB 2.0. Realistically speaking, you may not get this speed owing to a variety of factors, but you can always expect it to be 4 to 5 times faster at the very least.
Therefore, if it takes you about 10 minutes to transfer 5GB of data using USB 2.0, it will take less than 3 minutes to transfer the same data with USB 3.0. If you regularly transfer lots of data between devices, USB 3.0 can save you a lot of time.
Note that you can recognise USB 3.0 ports easily because they are usually blue or have the 'SS' (Super Speed) logo on them.