A general comment:

The N9 on Meego is not a Google phone on Android. Everyone switching will have to accept some things will work differently and be willing to get used to the new way.

If you expect e.g. maps and various other apps to work exactly like you know from Android, well, then you should get (or keep) the Android.

As for maps, for example, Nokia bought their own mapping company (Navteq) and therefore doesn't rely on third parties for their mapping apps. (Did you know Nokia even has their own desktop map site from that?) Google relies on third parties like TeleAtlas for map data. Because Nokia owns the data and technology, they can offer things Google can't, the biggest one: free offline maps. AFAIK, you can download a 10-mile patch of map around your destination on Android, but if you want more, you have to pay. Nokia lets you download and install the entire world if you have enough space on your phone, or break it down by country or state. I used it recently on a trip to Death Valley, far away from any mobile phone or WiFi connection - awesome. Having all maps preinstalled also makes zooming super smooth. You can actually see streets and place labels re-arrange themselves crispy-clear in real time as you pinch your fingers, no waiting for the next zoom level of tiles to load. I actually think the Maps app is one of the N9's best showcase features and that it'll withstand any comparison to Google maps with ease.

As for Foursquare, I'm not using it, but there are several clients on the Ovi store with good ratings, including an official app. I'd be surprised if you didn't find something to suit your needs.

Edit: To answer you specific question about sharing locations:
Tap and hold on the desired spot on Nokia Maps, nearest address pops up, tap address, it goes to a Neighborhood screen for that location with a list of nearby shops, restaurants etc. and a few more functions, one of them is a Share button that lets you send the location via any account you have set up (email, IM, Facebook, Twitter, SMS etc.)