I don't know what this one does, but it takes your dashboard version from 2.0.14717.0 (the update released the other day) to 2.0.14719.0. I can't see any differences and in the UK we still don't have that new style Marketplace yet.
I just got it too. I'm in the US though. Looked around and only noticed one minor thing. With the last update, in the app area, the social tab was there twice. Now it's back to normal. I doubt that the update only changed that though.
Xbox LIVE Trial Subscriptions require a payment option and automatically renew into a paying subscription.
When someone signs up for an Xbox LIVE Silver membership, they will be offered the option to purchase an Xbox LIVE Gold subscription. If they choose to not purchase an Xbox LIVE Gold subscription, they will be offered an Xbox LIVE trial. If a user selects to move forward with that trial, the user will be prompted to add a payment option and will be set to auto renew into a monthly subscription at the end of the trial.
This aligns the Xbox LIVE subscription with the current Zune Music Pass subscription, in the trial sense.