According to the Guardian, Twitter growth has stalled before, only to recover the next month. (See the second paragraph of this story, which also reports that Twitter has made reporting spam easier by adding a “spam” button to tweets.)
But I suspect the novelty has worn off Bing! An excerpt from the Reuters story:
After picking up decent market share every month since its June launch, Bing grew its share by a meagre 10 basis points last month. According to comScore, Bing’s share of the U.S. search market grew to 9.4 percent, versus 9.3 percent the month before.
Google widened its lead to 64.9 percent share, from 64.6 percent in August, while Yahoo fell to 18.8 percent from 19.3 percent the month before.