Unfortunately, I don't like it at all. The whole thing is based only on the Skype API, meaning it's forced to call a *.exe to establish contact with Skype, meaning also that it's impossible to see your contacts in the skype toolbar if skype is not launched yet, meaning it takes AGES to launch skype AND initiate a phone call.
The whole skype API is a big mistake. The whole thing, to be nicely cross-platform and easily integrable to other apps, should be purely XML-based. And not based on socket-based protocols. The client-side API should rely only on XML messages posted into file queues. The contacts list should be more parsable than it is today, contain contact properties instead of storing them into binary data. The logs should be XML-based, etc.
In conclusion, yes, this is a cool extension that may eventually become a major hit, but I think the Skype API lacks, like the protocol Skype it is built upon, openess. Because of that, SkypeFX is not as cool as it could be, as efficient as it could be. Call me a grouch, but that extension is a semi-failure from a usability perspective.