http://www.businessinsider.com/exclusive-qa-arrington-says-t...
Michael Arrington gave an interview to the Business Insider today where he discusses this issue, and also raises the (legitimate) point that conflicts of interest in journalism go beyond monetary investment and touch on personal relationships between journalists and the subjects they choose to write about.
http://www.siliconvalleywatcher.com/mt/archives/2011/04/like...
Veteran tech journalist Tom Foremski spells out the more traditional objection to journalists investing in the industry they cover:
"It's about protecting a trusted relationship between reader and reporter, and equally important, reporter and source."
[EDIT for clarity and grammar]