Everyone knows that the iPad 2 is going to be big.  Huge, even, depending on your definition of the word.  And now an analyst’s estimated that Apple will sell 600,000 of the devices this weekend, twice the number of first-generation iPads that sold in its first weekend of availability.

Analyst Bran Marshall of Gleacher & Co. isn’t alone in that belief.  Bloomberg’s Adam Satariano, who interviewed a few experts, stated today that he’s “one of several who expect the iPad 2 to outpace its predecessor.  Apple sold 300,000 of that version in 24 hours.”

Meanwhile, Forrester – which predicted earlier this month that the iPad 2 will claim a U.S. tablet market share of 80 percent in 2011 – reasserted its confidence yesterday, indicating that Amazon represents the only possible competitor.

It’s hard to doubt these forecasts.  Even if Apple’s tablets haven’t achieved mainstream popularity, they’re fashionable enough in certain circles.  One good example: some people who paid lots of money and traveled hundreds of miles to attend SXSW will spend at least part of today standing in line at a popup Apple store.

So count on seeing some very interesting sales reports and/or rumors as the iPad 2 becomes available for purchase.

One interesting side note: eBay’s stated that sales of the original iPad are also skyrocketing (instant sales have increased 796 percent week over week) ahead of the iPad 2’s launch.