Phone calls, wEb browser, wifi, 3G, Sms all work.
I haven't managed yet to install any apps that aren't already present out-of-the-box via the built-in app managers. I'm sure though there is a couple methods downloading the files and doing things manually. Many Meego apps are proven to work as-is under Nemo on N900.
What most keeps me from using it now is that I have a german keyboard on 'N900 an currently there are only English and Russian locales available, also in the vkb.
Also, I couldn't get the camera to work.
Task management is also still awkward. The basic mechanism (slide inwards from the side) being elegant, it doesn't work in all apps, and I'd really like a hardware keyboard shortcut for it.
Everything looks pretty cool to me, I like the design a lot and tons of updates are being provided every week.
Some of the problems I'm listing here may be due to my ignorance or already obsolete.
However: to me Nemo it's still far from ready for everyday use (and development is not aiming to make this a priority in time), too many things still missing that I require daily as a power user and there are working solutions for in Maemo.