My experience so far with my Handtec supplied N9 has been pretty much identical to the_Wildgoose also. I've not had a crash or a hang though I do get the occasional slow down, particularly when it can't find a 3G signal.

The office here is in an old gritstone mill with thick walls and barely any phone signal gets in. My N9 (on Three) is often stuck saying 'Emergency Calls Only'. My C7 used to hold on to 1 bar btw so I'm not sure if Nokia's all polycarbonate body is of great benefit for phone signal strength. You regularly see phone owners (iPhone, old Nokia, HTC, all networks - doesn't matter) run for the door to stand outside the building to get a signal.

Mine is also running a SIP account (sipgate) and Skype and Twitter and Facebook + 3 IMAP4 mail accounts. There's 8-12 open apps running. The SIP account has been pretty flawless once I worked out to use a different port to the 'landline' SIP phones in the office.