A source speaking to Eurogamer is "confirming" that Borderlands 2 is in development at Gearbox Software. The same source is saying an official announcement is coming soon, and the game will release in 2012 on the Xbox 360, PC, and PS3. Someone else's source doesn't normally have much clout with us, but Eurogamer is the largest video game site in all of Europe (hence the name).
If this is true, Gearbox Software is keeping very busy. That would mean they're simultaneously working on Borderlands 2, Aliens: Colonial Marines, and Brothers In Arms: Furious 4.
Europe's version of E3, Gamescom, is just around the corner, which could serve as a likely venue for such an announcement. Or publisher 2KGames could make the announcement whenever the hell they want. Either way, we'll keep you posted on any announcements if and when they're made.