Powering a WS2812B strip
I built a screen (total of about 240m @ 60/m, divided into 4 panels) for burning man. Each strip in a panel was 75 LEDs long (1.25m). I tied 8 of the strips together at the ends (so 8 strips of 75 LEDs in parallel) and ran two of these sets of 8 off of one power supply. I calculated out that at half power, (128 to each color for the entire set of strips), 8 strips (75 LEDs x 8, so 600 LEDs) took about 8.5A @ 5V. I used a cheep Chinese 300w smps (well, a total of 8 of them actually). 
But ya, the Arduino by itself won't do the powering. It can drive the data line just fine (since technically it's only pushing the data to 1 2812). 

So as a suggestion, make sure you power each 1m strip individually instead of tying them all together and having every LED in parallel (and the strips themselves in series). What I mean by this is, tie the +V of all the strips together to one power wire, and then tie all the grounds together. Don't just line up all the strips in a single line, end to end, and solder them. Just the data line should be like this.

You will want about a 40W power supply (for 8A @ 5V). And try to avoid turning them on at 255,255,255 (full brightness) as then tend to use a lot of power and get really hot. You can get a Chinese power supply for like $10 from ebay that will power it for you.

PS. My avatar is a 16x16 panel of those WS2812B strips @ 60 LEDs/m