The average person doesn't care about any of this stuff.
For my part, some of their plusses are actually detractors.
Removable battery? Every phone I've had was rickety and ended up with a broken battery cover (I wouldn't consider myself hard on electronics) and a bunch of lint and dust inside the phone. 4+ inch screen? Seems big and it's lower resolution, I prefer higher DPI in a smaller screen that can fit in my pocket without making a big flat bulge. And lastly 4G = battery drain. 3G where I live has great performance and I often use the personal wi-fi hotspot and for regular browsing and email and stuff I have only good things to say.
Also imagine the space you save by not having a user serviceable battery compartment. No latches and contacts in a little plastic housing and walls to separate the battery from the rest of the device. You can make it any shape you want and fill the entire device.
I don't think giving away those benefits are really very worthwhile in any device I own. That includes everything from my toothbrush to my laptop.
Also, not having to pay an extra $100 or $200 for more capacity, although they probably "don't care" in that they just buy the smallest iPhone.
Then makes them go "crap" when they're trying to walk and text with one thumb.
4.3" screen (the Fusion edit: make that "Infuse" is 4.5") versus 3.5" screen is a massive difference.
Apple pushes Facetime yet Samsung SGII has front camera with 2MP 1920x1080 versus the iPhone at VGA 640x480 (.3MP)
Vlingo is pretty darn good too.
Although Android has to fix stuff like this http://i.imgur.com/mGwxD.jpg
If it's a smartphone I would say it's main purpose is to view websites and use apps such as Facetime or equivalent which would be uncomfortable on a small fuzzy screen.
Some day we get the roll-up displays and have scroll like phones with large folding/roll-up screens.
My claim is: 3.5 inch screens are a good compromise, allowing for comfortable browsing, reading and writing. The additional screen space would never be worth the additional bulk (also: uncomfortable one hand use) for me.
That's all about personal preference.
Someone with an iPhone would be used to the "hand feel" of a 4" (101mm) iPhone if the screen bezel were thinner.
It is odd that there isn't any ready-to-go Samsung app for it (I have an SGII) or at least I didn't see one yet.
It's not a big surprise though since not all phones which use the Android OS have a front facing camera so it would be up to the individual phone manufacturers to add an app if their phone has a front camera.