NEW YORK/LONDON (Reuters) - General Motors Inc's decision to stop advertising on Facebook may be a wake-up call for the No. 1 social network, but Top advertising executives say it's far too early to know if the site will take off as an advertising platform. "There's a lot of potential but it's not a slam-dunk," said Martin Sorrell, chief executive of WPP Plc, the world's largest advertising agency. "Showing the impact of branding on Facebook is going to take a long time," he added. Facebook is due to begin trading on Nasdaq on Friday in an initial public offering that will raise about $15. ...

Google on Wednesday began making its search engine smarter, in what the Internet giant called a major upgrade that looks beyond query words to figure out what people are actually seeking online.

NEW YORK (Reuters) - Investors who want Facebook Inc shares when the No. 1 online social network goes public later this week may have lost the opportunity. TD Ameritrade and Fidelity's brokerage arm both stopped accepting orders of Facebook shares as of Tuesday evening, according to representatives for each of the companies. Morgan Stanley & Co did the same, according to three advisers at the firm who declined to be named because they are not authorized to speak to the press. E*Trade Financial also stopped accepting orders as of 4 p.m. ...