• Sales estimates: Most analysts were cautious, fearing perhaps that whatever they wrote would soon be overtaken by an Apple (AAPL) press release. Most, like Piper Jaffray’s Gene Munster, stuck with 500,000 units. But Baird’s William Power estimated that Apple sold “roughly 1 million” the first weekend, Wedbush’s Scott Sutherland “wouldn’t be surprised” by that number and Global Equities Trip Chowdhry thought Apple “may have sold” three times as many iPad 2s as iPad 1s its first weekend, which amounts to the same thing.
• Line counts: A lot of headcounts this time around. Munster’s team counted 1,190 at Apple’s Fifth Avenue Store. Ticonderoga’s Brian White thought he saw 2,000 to 3,000 at the same outlet. Hudson Square’s Daniel Ernst counted shoppers at two Apple Stores and two Best Buys in Manhattan and got a total of 2,300.
• Store supplies: Apple’s own stores — where there are no middlemen to share its profits with — had the most iPads in stock, but nobody seems to know how many that was. Best Buy (BBY) was more forthcoming. The outlet where one of Cross Research’s principals (Shannon? Robert?) bought an iPad on Day 1 had 80 in stock. According to Global Equities Chowdhry, it took each of the three Best Buys he called 4 minutes to sell their entire stock of 40.

• Competition: Deutsche Bank’s Chris Whitmore spoke for many: “The iPad 2 consolidates Apple’s position as the innovation yardstick within the tablet space and we expect it [to] dominate the segment. We remain cautious on the non-iPad segment of the tablet market and expect new entrants to struggle gaining traction in the market.”
• Bubble ahead? “We reiterate our view that there is risk of a tablet bubble in 2011,” writes Morgan Stanley’s Mark Moskowitz. “There are many competitive tablet entrants expected, but so far, we think that both Samsung and Motorola have experienced disappointing adoption curves. We expect more of the same from other entrants. Meanwhile, Apple’s iPad 2 technical and form factor improvements, coupled with opening weekend stock- outs, point to a widening gap in market share ownership potential.”

Also on Fortune.com:

• Piper Jaffray: iPad 2s totally sold out; 70% to new buyers
• Inside the iPad 2 gray market
• Video: Walking the longest iPad 2 line

[Follow Philip Elmer-DeWitt on Twitter @philiped]