Marketing Magazine posed this question to me and three others last week. See my answer below and follow this link to get the other answers The Marketing Society Forum.
Ads will benefit Twitter. Last November, it changed its key question from 'What are you doing?' to 'What's happening?' The answers form a unique searchable database. Twitter is a real-time search engine - the fastest and most relevant way of finding out what's going on right now. This forces Google - worth £114bn - to reappraise its strategy. High stakes indeed.
Twitter knows that in the past, brands like Yahoo! got it wrong, by over-commercialising their online real estate and not balancing user and business needs. Google launched as its antithesis and honed its design, shunning banners for pay-per-click text ads. Discrete sponsored links are now an accepted part of the visual language of search.
Each web innovation creates a fresh generation of purists who gradually or grudgingly accept mainstream commercialisation. This is no exception.
Twitter has learned from its predecessors. It will emerge more useful, and the incremental income should fuel a new wave of innovation.