As a current Tab owner, and an incredibly AWESOME hacker (not really, just a minor tinkerer of gadgets), I think I might be in the right spot to share my experiences and opinions. KEEP IN MIND: I'm in the United States and I own a Verizon branded Samsung Galaxy Tab. If you're in Europe, you're FAR better positioned than I am (telephone functions are disabled in the US versions, but can be hacked into the T-Mobile version, so far). I can't remember whether you're in the US, etuoyo, and I didn't see your location listed in TMO's profile for you.

It doesn't come with a wired headset, nope. Mine certainly didn't anyway. Although, stereo bluetooth headsets are getting so cheap, why not get one anyway? The Motorola headsets I mentioned a few posts ago only costed me $35 and they work for stereo audio listening as well as telephone and they SOUND great (both to listen to, and the microphone for calls). In either case, remember that the US tablets can't make phone calls.

Yes.

No. Skype's fault--no Android device will do Skype video calling.

Well, the question is a misdirected one. The reason question here is, does the N900 have a transfer contacts option? Or even an option to export your contacts to a vcf (vcard) file like Apple, Palm and every other device (including the N800) have done for over the past two decades? If so, then you could upload your contacts to http://contacts.google.com. Once they're in your Google Contacts list, they'll automagically appear on your Android device.

According to Google Contacts' "import" option:
We support importing CSV files from Outlook, Outlook Express, Yahoo! Mail, Hotmail, Eudora and some other apps. We also support importing vCard from apps like Apple Address Book.

At worst, you can add them via http://contacts.google.com manually--although I find it hard to believe such an open-source device as the N900 wouldn't allow you to export as vcf or csv or something.

Yes, you may use any image as your wallpaper.

Yes and no. I believe there might be one using a Samsung flashing tool running in Windows. Since I don't have any Windows computers, this effectively means a resounding no for me. ...yet. Clockwork Mod is working on (and already has a beta version out) their rescue boot tool, which I already use on my Motorola Droid. When you reboot the device you can hold down a combination of keys to get to what might seem like a sort of grub menu that kicks in before Linux loads. From that menu, you can do a bunch of stuff, including running a compiled-in tool called nandroid which lets you save or load a state image of the device as a backup from the SD card. With that tool, no matter HOW bad you f*** things up, you can restore your system bit-for-bit back to its previous state right from a tool that runs effectively at what might be something of a BIOS level before the OS loads. Clockwork Mod ALSO gives you the benefit of applying downloaded ROMs right from the menu, too. So, no need to connect the tab or handset to a desktop to do all of this, like you've been used to doing with the N900. The Android platform is truly far more independent of the need for a desktop computer than Nokia's ever was.

Still, this Clockwork Mod with nandroid is a work in progress as far as the Tab is concerned. So right now the answer is still sort of "no", unless you have Windows and get the Samsung tool and get the Samsung image from the XDA developers site. Not worth it, in my opinion. I'll wait for Clockwork Mod with nandroid, myself.

Despite that, I've still rooted my Tab but I'm very careful with what I do (I don't apply any customizations, as few as they are, for example). If you simply USE your Android device and use just Market apps, near as I can tell there's virtually no way for it to become corrupt enough to need a firmware flash and inconceivable to imagine bricking it.

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I hope I've answered your questions and concerns sufficiently, but please feel free to shoot me back a reply to see if I can flesh out anything or answer any other questions you might have.