I was a confirmed n810 user until Google I/O last year when Google tempted me with an Android phone and I pretty much abandoned my n810 overnight. Nearly, but not quite completely. There are a few, a very few things that the n810 does better.

Skype. Android has Skype lite: what this means is that whenever you make or receive a Skype call you are actually making a real telephone call to Skype and it goes over the Internet from there. This is great: compared with the n810 you get better sound quality and no dropouts. But, you also get charged for the phone call. In San Francisco last year Google gave everyone a 30 day SIM card so I was able to Skype back to my wife in the UK while cycling across the Golden Gate bridge(!), if I were to go back to the US again I'd be using my UK SIM card and using Skype would require an International call at £1/minute. So, Android+Skype is excellent if you don't pay for local calls and you aren't roaming. If you pay for calls, or worse are roaming, then find a friendly wifi connection and use the n810.

Maps. Same story really. Android does maps really, really well. That is, provided you have a data connection. If you're overseas and not connected to wifi then forget it. n810 maps aren't as good, but they don't require a connection. So, when I was on holiday last year the phone was barely used, it was the n810 I used for maps.

If you don't go overseas then neither of these may matter to you. For me they matter but Android still wins hands down.