I currently own a site about cell phones news, which is almost a year old. 95% of my pages are indexed by Google and all articles are picked up by Google News.
I now want to add more tech news, but don't want to mix it up with the phones. I purchased a new domain but I don't know if I should start writting there or create a subdomain ... It may take months for the new domain to get indexed by Google.
If the tech news is related to phones I would suggest a subdirectory approach and avoid the subdomain. Think down the road when you have developed that news section..wouldnt it be nice to get inbounds links to your main domain , rather than a subdomain ( effectively a seperate domain in all but a gaurantee to avoid the sandbox ).
I speak from experience. I am soon to aggregate my subdomains into my main domain. I believe in the linking strategy , there is a glass ceiling on the number of good links you can get to a purely commercial site , whereas if theres " juicy " stuff in that domain ( your news ) you stand a higher chance of breaking that glass ceiling.
If the tech news is about widgets and not phones .. then of course a seperate domain and forgive the digression.