I have been testing different versions of Nokia Chat and now Contacts on Ovi and while the software itself is a decent XMPP/Jabber client with additional functionality I myself do not really want to go the trouble of having to invite and convince my friends to join yet another messaging service. I know that I can also ask them to accept my OVI account as a yet another friend but all this is annoying since I did not want yet another XMPP/Jabber identity in the first place.
What I really needed was the decently made and network access point utilising IM client, where I could configure my various existing identities in Google Talk / Microsoft Live Messenger etc. The Contacts on Ovi succeeds in making that first part, decent and network access point utilising IM client for S60. It however fails to deliver even the same kind of functionality as the instant messaging client on N810, which can have multiple accounts and in the future also multiple plugins for connecting to various other Instant Messaging systems. That is the way I think instant messaging clients (and email clients) for mobile terminals should be done to be useful.
I can understand that having only an OVI account is probably more of a business decision, where Nokia wants to have a control point, which ties the customer more directly to Nokia services. The same thing applies to Nokia messaging, but this decision is also a key issue why I do not see Contacts on Ovi or Nokia Messaging worthwhile applications and services to use.
Technology good, implementation of the service not so good.