Is it just me or does it seem like  singing is a good bit harder in this game? 
 
i cant seem to make the pitch arrow move as well as i can in rock band 2.. Maybe my already shitty singing voice is just slipping...

I'm positive that the singing is more strict in this game, which doesn't surprise me at all, since a key feature in this game are the vocals.

The solo singing seems about the same to me, but the damn harmonies are kicking my ass. I can't imagine singing while playing another instrument on any difficulty above medium for vocals.

Only players on the same Xbox as you can sing harmonies in an online match with you, probably for some kind of latency issue.

My question for singers would be... 
 
how the fuck do you do it? I can't sing worth a shit.

Well apparently they removed the use of 360 headsets because it doesn't offer as wide of a range for vocals as a mic does, so that would mean they force you to be more accurate this time around.

I'd say that compared to Rock Band and Rock Band 2, the vocals are less forgiving.  Harmonies are really truly a challenge, though!  My wife and I can both sing pretty well, but we've only been able to get all the double fabs in a song once, on hard or expert.   
 
On a related note (bad pun), I noticed that they somehow fixed the microphone lag.  In RB 1 and 2, I always have to start singing the note a little before the note actually happens because of the lag (even though the other instruments are calibrated fine).  It's the same delay that's audible during drum fills.  In Beatles, I don't have to start singing early.   
 
The awesome thing is how good you get at singing after working on harmonies for a while.  This morning at work I was able to sing Something and identify all the harmony lines in it.  It was really fun to be able to do that!

also, makes you realize how impressively talented all of the beatles were. they would play melodies on their instruments, sing lyrics, and harmonize them all at the same time. multi-tasking at its finest. 

Have definitely noticed this, especially when singing and playing bass/guitar at the same time on expert. I'll still pass the song, get around 95% on the bass part, but around 75-80% on vocals. 
 
If I just sing vocals on their own, and focus on where the indicator is at, I can get in the 90%-range, but, yeah. As a person who knows a lot of these songs off by heart, and has sung a bunch on RB1 and RB2, this is totally less forgiving. 
 
As for the harmonies part, I think that for the person that picks vocals, everyone else singing vocals has to be local to that person. I don't see a way to have multiple singers under different gamertags online.

In story mode, did anyone notice that for the last song in every chapter, the pitch detection is more strict?  Last night I finished Chapters 1 and 2 on vocals on hard, and on the fourth song in each set, the pitch bars were noticeably narrower.  The first time this happened, I thought I moved up to expert by mistake, so I restarted.  Nope, still narrower pitch bars.

strange i found singing in beatles easier than in rock band

I found them easier. Using two mics I could even get my own double fabs in Back in the USSR and a few other songs.