I put CAT6a permanently along the corner of my ceiling/walls beneath classic mouldings in a 1920 flat. It was a lot of work but wireless is out of the question in old brick buildings:
Network cables vs. mouldinghttp://www.flickr.com/photos/sigg3net/4786886982/in/set-72157622689373755http://www.flickr.com/photos/sigg3net/4762777727/in/set-72157622689373755
I learned quite a few things. CAT6a is so far only adopted by large enterprises AFAIK. All my equipment is consumer equipment and therefore CAT6(E). When or if CAT6A equipment becomes available cheap is a good question. In the meanwhile I have bandwidth I cannot use since all my (granted, old) machines are CAT6E or plain CAT6.
However, if I had run tubes (like electricians use) instead I would be able to buy cheaper CAT6E cable at present and simple pull new CAT6A cable when it became cheap enough or when need arises:http://www.carl-ras.dk/gfx/imager/catalog/55622010.jpg
It would not have worked in my non-insulated, brick building flat however, since there is no hidden room between outer wall and inner wall. So I'm quite satisfied. The CAT6A cable also has a tougher sheath so it wasn't harmed by rough handling during construction, and sports better anti-cross-talk measures. If you can run tubes and pull wire through them, do so. You can then buy cable according to budget. I paid 3-4x the amount I would have paid for regular CAT6 because I knew it would last some 15 years. But they cannot be replaced.
Network cables in stripped flat:http://www.flickr.com/photos/sigg3net/4741380285/
After some plastering:http://www.flickr.com/photos/sigg3net/4786888822/in/photostream/