Skype may have a good relationship with Facebook, but their products are still indirectly competing. Now that Facebook supports one-to-one video chat, I have no reason to download or register with Skype. Facebook went through great pains to keep user data anonymous from Skype. If Facebook is successful in getting its users to video chat, Skype will effectively become just a technology provider. Once that happens, Facebook could replace the underlying Skype technology with something developed in-house, thus killing Skype entirely.
Of course, given the good relations that Facebook has with Skype/Microsoft, I doubt they have any desire or intention to kill Skype, but the two services are certainly competing for the same users now.
Facebook's video chatting feature has no influence on my decision to use Google+, but it does influence my decision to use Skype.