Hi dan,
I hope my input can help you with your decision, I am just going to express some of my own experiences on the matter (and maybe vent a few of my strong opinions also
).
I will start by saying I just bought my self a nexus one maybe 2 weeks ago to replace my ip3g (which i am still waiting to for to become unlockable on ios 4.1
) and I must say, I am still soaring higher and higher on the wave of "Damn my new phone ROCKS!!!" (ESPECIALLY compared to my ip
!!! ).
Anyway here are some of my opinions on the matter. First off, whatever a full featured Android 2.2 phone may not do now, it can and will do soon. The reasoning behind this is that the hardware is not third rate, crippled, incompetent, or outdated so its potential is only left to be determined by the software and the OS, and here you have a categorical difference with Apple. Although the same principle still aplies, Apples OS is prided on its restrictive incapacitating death hold which stands between you and the full range of (potential) functionality of the hardware. And this is a very important point. Basically, if the hardware is similar, the only important area to determine which is better is in the OS.
The only thing at this point, hardware wise, that is unique to an ip4 vs. a leading Android phone is the retina display and most likely the front facing camera (unless you are looking at the Evo 4g). Other than that ip4 hardware specs are likely matched or more likely bested, pretty much across the board. What this means is that the only really important thing to consider to determine the phones capabilities is in the hands of the apps and the OS. They are the real tools that will determine how much you can actually take advantage of the cutting edge hardware you payed so much money for.
This principle is clearly in favor of Android, and here are a few of reasons why. The first is "policy". What are Androids policies? and what are Apples? If you look at this in principle, whos potential is greater? And who will inevitably grow bigger (i.e offer more)? THIS IS A NO BRAINER!!
People can point out that the iphone app store is 5x the size of the android market, or whatever (250,000 vs 50,000+ / who really knows?) but this is misleading and about as useless as 90% of the apps in the app store (btw the Android store is also full of useless apps), but because people use this idea to try to trump up the App Store, let them carry it through in its entirety. (30,000 flash lights, 40,000 notebooks, 15,000 fart simulators, 20,000 beer mugs that empty when you turn your phone sideways, 30,000 silly face makers... please )
Anyway my point is Androids policy i.e open source, will naturally allow it to surpass the app store – and at an exponential rate. And this is not just a matter of increasing useless junk apps but the actual range of functionality that the USEFUL apps will be able to achieve is basically unrestricted and unpredictable. This is a difference in "Policy", not a measurement of stock piled novelty apps that are the equivalent of intentionally downloading spam unto your phone. And look at the time the app store had to grow, now compare that with the rate of growth of the Android market. Now compare that with the inovation and revolutionary nature of the useful apps in the android market. Really there is no comparison. The option of 30 different ways to turn on a flashlight on the iphone vs the option of 30 different ways to manage mutitasking on Android are not equal in value. Believe me.
Once you get accustomed to using widgets on your home screen and configuring your launcher/springboard of choice to your liking, you will not be able justify spending so much money on an iphone which should be able to do all these things BACUSE THE ACTUAL HARDWARE IS CAPABLE but doesnt because Apple didnt make it that way!!!
It really makes you wonder wtf all your money is really going towards! (besides Jobs pocket
)
The only function of my iphone that i actually miss is the app "netflix" (maybe only in the US, Iam not sure), which is already in the works for Android....
I also think it is unavoidable to take into consideration the never ending infuriating headache that is re/jailbreaking and / or unlocking the iphone as more and more crippling firmware continues to be released. This will unquestionably compound anyones appreciation for the Android platform.
It is important for you to consider that even if the ip4 is a fast device, after you jailbreak and install various cydia apps you are likely to be facing lags, hang-ups, restarting, restoring, freezing, rebooting, 30 min apple logos, loosing your unlock, stuck waiting for the next release of redrain, bluerain, whitewash, or red-tape to be released, need I continue?
In my honest opinion owning an iphone is paying extreme prices to buy your way into a never ending battle with company that makes it, in an attempt for you, the owner, to be able to do what you want with it.
wtf. As of today iOS 4.1 (i.e any ip4) is still not unlockable and people who may have payed close to $1000 for it are stuck with a phone unable to perform the essential function of making a phone call on their preferred network.
I guess I could go on with a few more points, but I will stop here, as this is already long...
I will just say this, Android is awesome. I never fail to be impressed every time I pick it up (and that is even with a 5x smaller app store). If you go for an Android phone get most cutting edge one you can find (i.e Desire, Evo, Droid X, etc) because it will still be much less than an unlocked/free from contract iphone4, or one with a contract after you factor in the contracts overall costs. And Get Froyo 2.2. All the features you asked about; mail, keyboard, etc are fine and will continue to evolve past your expectations faster you could have expected.
Hope this helped
unlikely 
