These will have more significance in the near future in terms of search bots and seo to define your content and target audience.
Coming back to this, the search engines are not going to suddenly start crapping all over the .co.uk / .com domains because they are not instantly identifiable with the type of business/media you operate within.
It may be beneficial to minor degree for a new website but long established sites using a .com or .co.uk wont suddenly start seeing their rank go down because of a plethora of new domains being available.
Id go so far as to say if I see a company operating under .biz I instantly assume they are a bit of a cowboy outfit in fact, a view not helped by some of our clients opting for such as domain. Its up there with lawyers4u type names