Well, I'm actually switching to an E90 from an iPhone as of today. In the US, the 3G on the Nokia won't work, but here was what sealed the deal for me:
1) Physical keypad on the front of the Nokia. I hated not being able to dial by feel on the iPhone. For sheer phone functionality, I much prefer the dedicated physical interface. The iPhone has a great dialer for a touchscreen, but to me, real keys win out.
2) Camera. I like to use my phone camera for quick snapshots all the time, and there's simply no contest between the 3.2mp/AF system on the Nokia vs the fixed-focus 2.0mp on the iPhone. No shocker there.
3) Physical QWERTY keyboard. Much faster for typing just about anything.
4) Removable battery/storage. With 16gb cards now available, I'm flexible for storage on the Nokia, not to mention I can swap it. For the time being I've just got a 1gb card I got from a friend, but I might upgrade it later. So far as the battery is concerned, I presume it goes without saying why a user-replaceable battery is advantageous.
5) Symbian S60 has a much more open developer community--I know that the iPhone SDK is open to all, but it's nice to get whatever software one wants without having to worry about Nokia or ATT trying to protect business interests by limiting applications (for example, consider Apple's stated policy regarding applications running in the background...)
6) Ultra-high res. screen. This is mitigated somewhat by no touch screen, but I'd rather use a directional pad to move a cursor than constantly have to wipe fingerprints off my screen...
I'm aware that I will be carrying a significantly larger, bulkier phone with a UI that is not as slick (however more powerful IMHO). The iPhone is a beautiful piece of hardware, with an incredibly slick GUI. It's the perfect smart phone for the user that is satisfied with what comes preloaded out of the box, or for beginner users. (Yes, I know about/have jailbroken an iPhone. It works, but the overall content available is still nowhere near what's available for S60...plus, try using SSH without a physical keyboard...yeesh) No offense meant here...trust me, I consider myself a power user, and originally picked up an iPhone on launch day over a Nokia smartphone. That said, while I was totally comfortable with my dad going cold-turkey to the iPhone with limited/no help from me/others (not by choice, simply by the fact that I'm away at college), I wouldn't dare put him on an OS that is as complicated and (yes, somewhat less intuitive) as Symbian S60.
To sum up: The iPhone is a beautiful, powerful device. However, if you plan on lots of typing, find an alternative with a physical QWERTY. If you want a legitimate point-and-shoot camera, the iPhone works, but not well. If you want to dial without looking, get something with a physical keypad. If you're concerned about having apps that Apple/ATT/O2/whoever your local iPhone service provider might not want you to have, get a Symbian phone instead (VOIP on cellular data connections, etc). If you don't want to have a sealed battery/fixed storage, find something other than an iPhone. BUT: if the above don't matter to you, and you're looking for the sleekest, prettiest, easiest to use device on the market, you could hardly do better than an iPhone.
Obviously, the N95 and the E90 aren't the same device, but basically everything but the QWERTY and the high-res internal carry over from the E to the N.
I know this post says a lot to criticize the iPhone, but please don't think I'm trolling...as I stated before, I bought an iPhone on the US launch day, and used it daily until this weekend...and I still think it's a great device--just not what best suits my uses for a smart phone. Again, don't let me discourage you from an iPhone if you really want it...I just figure (from experience) that one is best served by matching the strengths of each device to what you really plan on doing with your phone. Good luck!
EDIT: Oh, and as far as web browsers are concerned, I've found the E90's browser (same as the N95) to be nearly the equal of the iPhone's...no tabbed browsing on the E90, but it can actually set/remember a home page

So far as rendering is concerned, I've come across very few differences.