I have Fring on mine, but I only use it for text chatting, not used it for video but it seems ok
Text chatting works ok on the N8 and improvements have been made to video calling. Not as effective as Skype VC but until thats available Fring is what I use. It's 'adequate' but not great.
Couple of issues I have -
There is no notification of new messages displayed on the phone - you must go into Fring to check -
would be good if the N8 application button/light flashed (only does so for sms messages or missed calls)
If you close the chat screen and go back into it - you lose the text from your conversation.
Voice calls/video calls - so so
Chat - adequate
GT