Apple will do as Apple has done for years with the iPhone and iPod and introduce the iPad2 either on the day it is ready for sale or at most a week ahead of time.
As soon as they reveal it the main press will shout about it everywhere and even mainstream consumers will stop purchasing the iPad1 and wait for iPad2.
However, what nobody has mentioned yet (as far as I have read) is Apples Annual event to discuss the next iOS release. To my memory this normally happens in March ahead of the iPhone release in the summer (happened in 2008, 2009 & 2010). What they may do this year is talk about iPad2 release at the same time they talk about iOS5 in last week of March ahead of a 1st week of April launch? Just my guess.
The question is - will iPad2 be released with iOS5 installed, or will it be released with iOS 4.3 and we wait until iPhone5 (June/July 2011) for iOS5 on iPad2?
That is my guess as well. As much as I'd like to see the iPad 2 now, that leaves a big gap between February and April. The original iPad had a ~60 day gap between announcement and availability, but that was a brand new product line.
March seems good for an April launch of iPad 2. March has also been the time of iOS preview events. It makes sense that they would roll it into one event. "Come see the future of mobile"...Talk about Verizon iPhone, the latest iOS 4.3, Preview iOS 5, reveal the iPad 2 for April release. Boom.