Nails look like they have been put in with a nail gun so there is a fair chance they are ( and they really should be) ring nails. Use tthem for roofing, studwork and flooring so they are fine for decking.

Some of them mitres look a little out though!

Go for hardwood decking if you plan on staying there forever and want it to last. Not cheap though, i bought 2x 4.8m lengths some time ago because i didnt pinch enough from work and it cost me over £40!!!

Gavin.

Edit.. it was this stuff but i paid more http://www.edecks.co.uk/shop/product.aspx?pid=158