One premium feature that's already popular outside the U.S. is custom avatars, says Larry Grothaus, lead product manager for MSN.

FORBES: Just Speechless

Karan Khanna, Microsoft's lead product manager for NT Server, explained that applications that run under NT 4.0 will run under Windows 2000 if they don't access the new features.

CNN: graphic

Around April, Mr. Costolo also brought on Satya Patel, a former Google product manager, to help lead product initiatives with Mr. Dorsey.

WSJ: New Financing Values Twitter As High As $7 Billion