I love, love, love the E90, and I'm going to keep using it until there's something better on the market. I've never used an S80 phone so perhaps I don't know what I'm "missing", but I think the E90's ability to work on the outer screen, flip the phone open and have everything instantly appear on the inner screen FAR outweighs any sort of PIM or "easy to use" advantages that the S80 phones might've had. S60 is more than easy enough to use, going from my E62 to the E90 took all of half a second to acclimate.
The E90 is a bit thick and a bit heavy, but it's also much narrower when closed than any WinMo slider, and it makes it surprisingly comfortable to hold while talking. Squarish phones like the E61 or Blackberrys are much less comfortable, I don't care how thin they are.
I think the dual screen clam shell form factor is perfect. The E75 with its shitty little screen and the N97 with its crap keyboard are PALE imitations of the E90's perfection. ALL sliders are flawed because the sliding mechanism takes up far too much space, and you're stuck with a tiny little 3 or 4 row keyboard.
Who would make a sliding laptop with a screen that couldn't adjust and the number row crammed into the Q-P row? Nobody. If a smartphone is trying to be a mini laptop, why should it be any different?
Last but not least, the E90 is hands down THE BEST gaming cell phone I have ever used. The E90 is a better GBA than the GBA. The big screen and the comfortable amount of space between the D-pad on the right and the left edge of the keyboard make playing Sword of Mana for hours fun instead of excruciating, as it would be on any other E series including the E75. You can have your iPhone, you can even have your nGage support. I don't miss it. Give me Quake 2, which the E90 runs beautifully.
Nokia, if you're listening, make an E95 with S60 FP2. Touch is not needed or wanted. Keep the form factor exactly the same, just give me N900 processing power, and keep the D-pad, no useless N900 arrow keys. Make the bezel around the inner screen smaller, and make the screen as big as absolutely possible. I don't care if its a bit thick or a bit heavy for the focus groups, I want a portable computer not a fashion accessory. And support for AT&T 3G would be nice. Charge whatever you want, I'll pay it.
Or, keep making phones like the E72 and N97 Mini, and my next phone will be from the first company smart enough to make an Android clam shell.