I agree with the last point, but not the first two. I use and carry both an N9 and an N900 (which I agree is slightly ridiculous...) since the N9 can't replace the N900 for a variety of reasons, but there are some things the N9 does much better, for example browsing mobile sites, reading and even writing email (SWYPE is great), instant messaging, usability when it comes to various kinds of feeds, and Nokia maps, especially outdoors in daylight.

For regular calls they are neck and neck, but for SIP calls I have found the N900 to be better, and SIP is what I use most of the time. I have had issues with SIP on the N9, basically calls breaking up or dropping altogether. Trying the same number with the same reception (either wifi or 3G) on the N900 has always produced better results. That's just my experience though; your mileage will vary.

Better out of the box battery life is true for the N9 I guess, but the point is moot because you can carry as many spare batteries for the N900 as you want with you and they are dirt cheap. I currently own 8, but generally carry 2-3 spares with me in my wallet when I'm out and about, where I don't even notice them. I always charge the batteries, never the phone, so I never worry about being attached by a cable with the N900 (and I do all my file transfers with ssh over wireless). I always have at least 1 spare battery to reach for when I need it, wherever I am. Basically I never even have to THINK about battery life with the N900.

The N9 is very slick and nice to hold in the hand with its unibody design, but the lack of removable battery is a huge pain, and at the end of the day the slickness and coolness of the phone's body just isn't worth this extra inconvenience. I find that the battery life varies hugely depending on how much I use the phone. I can easily get through two days with very light use; but with even moderate to heavy use suddenly I can't even get through the day; by tea-time the battery is finished. So I WORRY about the battery all the time with the N9, a huge downside to ownership and every night I have to remember to charge it. Having to worry about your device does not make for happy ownership. In contrast, I never have to worry about how much battery life I have with the N900, and I never have to remember to charge it. Whenever I wander past one of my chargers (there's one in the kitchen, another in the bedroom), with its prominent blue/red LED, seeing the blue light (means charged) reminds me to swap the nicely charged battery for the empty one I'm carrying in my wallet, which I do right away, and then forget about it again. It's a system that works really well.

If it came to an actual choice between the N9 and the N900 though I would find that very difficult. They have different strengths and weaknesses. I guess I would choose the N900 over the N9 at the moment, with a heavy heart, but this is only because there is much more software available for the N900 and it's such a mature device. There are things I simply can't do on the N9, but hope to be able to do as time goes on and more software is released. Eventually I expect that the choice will then go the other way - again with a heavy heart.

I guess I feel lucky I don't have to make this choice.