Twitter as Tech Bubble Barometer [ WSJ ] As Internet valuations climb and bankers and would-be buyers circle Silicon Valley in an increasingly frothy tech market, many eyes are on one particularly desirable, if still enigmatic, target: Twitter. Discussions with at least some potential suitors have produced an estimated valuation of $8 billion to $10 billion. Executives at both Facebook Inc. and Google Inc., among other companies, have held low-level talks with those at Twitter Inc. in recent months to explore the prospect of an acquisition of the messaging service, according to people familiar with the matter. The talks have so far gone nowhere, these people say.