When I saw clips from Kermit's big speech at the end in the trailers, when there are many characters, I expected a lot more characters to be there, just off-camera (mainly past the left of the screen). One of the later trailers showed a shot from that scene where there were a few more characters (like Trumpet Girl and that Grover-looking monster from a Meeting Film and Sing-Along Video), but those characters weren't to the right or left (I think they were blocked by Kermit or someone). We didn't really see past the right or left of that screen... All those articles mentioning that it has "every Muppet you can think of" and "100-150 characters appear" (I wonder if they were counting rebuilt puppets, because the number of characters I saw who weren't in the trailers was few... I know, others could be in deleted scenes, or maybe they forgot some characters).
The one classic character I am most surprised about who I didn't see show up is Pops. I'd expect many fans to know of him (he was in every episode in the last season and was heavily featured in The Great Muppet Caper). He showed up in Letters to Santa back in 2008, and appeared again in the OK Go Muppet Show Theme music video (and behind-the-scenes videos), so I guess he was in working condition then (it would be interesting if they'd rebuilt him right after the movie).
I wonder if the "every Muppet character you can think of" comment in interviews was really "every Muppet we can think of". Though I honestly don't think it's far-fetched for casual fans to know of George the Janitor, Mildred, Hilda, Timmy, Doglion, Mean Mama, Boppity, Gloat, Gladys, Louis Kazagger, JP Grosse, the talking houses, or Annie Sue (decided not to list any JHH or MT characters here). Fans may not know the names or personalities of all those characters, and today's kids might not know many of them, but I think those who grew up with the Muppets and saw The Muppet Show, movies, and TV specials would recall seeing some of them. The first season characters would be recognized by those who saw the first season episodes, Annie Sue was on the show quite a bit in later seasons (even if her personality wasn't developed much after her first few major appearances), Louis Kazagger had a prominient cameo in one of the movies, and most of those monsters popped up quite a bit on the show (and Timmy was in the opening... While I don't think casual fans would notice every Muppet in the opening, I'd like to think they'd remember all the big monsters in the opening).
Also interesting that the movie doesn't really have any "one-shot" characters, like Angus McGonacle, the Java Muppets, or the Hugga Wugga Muppets (I don't consider Mahna Mahna and the Snowths "one-shot").
Thinking of obscure character recognizability here reminds me of a time in the Ask Ken at Palisades thread when somebody asked about the chances if a number of characters becoming action figures and Ken Lilly doubting any of the ones asked about would become figures (and none of them did). I thought it was odd that he thought they were too obscure. I was of the mindset that some casual fans would recognize them somehow (and was also hoping that casual fans who regularly bought the figures would eventually buy every character in the line).