With OAuth and Facebook Connect are we heading toward a unified social platform?

No.

More nuanced answer: it depends on how you define “unified” and “platform”.

For example, perhaps the web is already, in one sense, a “unified social platform”. However what I suspect you’re referring to is seamless portability of your social graph and other personal information assets from one “site” or web application to another, without each site you use having to be aware in advance of every other site that you use.

Facebook has done a good job of this, but it is by no means the standard social platform that the web needs, since it is highly centralised, controlled by a single company and has more than a few “one-way valves”. Can you run your own “Facebook Connect” provider, and use that to provide your social data instead of Facebook? No? Then it’s not open or unified. It is, however, the best we’ll do for quite some time.

The intrinsic tension here is between the incentive/funds to innovate, an ecosystem of solutions, and useful degrees of standardisation.

Most commercial entities won’t enter a space unless they stand a chance of blocking others from owning the space – barriers to entry. Without such barriers, there are very few reasons to make the investment in engineering and outreach required to get the whole web on the same page (so to speak).

However, no “unified social platform” for the whole /should/ be owned by any one company. It should be a standard, ratified via the w3c or ietf or whatever, or at the very least an open and decentralised protocol with no proprietary encumbrances.

To be clear, I have absolutely no issue with what Facebook has done. It’s an inspired piece of engineering, doing what many others have tried and failed to do before (Microsoft Passport, anyone?). It’s just not the federated, standardised protocol that many people wanted. It’s going to take a while before such a system comes along, methinks. Two or three years, at least.