Google's DNS service: Google public DNS

Using google as DNS would mean they will see ANY DNS search or in other words they would know about any site you (likely) went to and so you provide them with a LOT of somewhat personal info, which they could collate with the other info they gather on you, make sure you are fine with that and be aware that if the law changes or there is some subpoena they could then be handing that info over to authorities who as you know will 'use anything you say against you'.

A quick comparison of Google Public DNS with OpenDNS (which has been around for a long time).

If you have to access sites banned by Google DNS (or, OpenDNS for that matter), you can skip these configurations when you hit a problem. However, most of the time sites blocked by OpenDNS (and, I have to still look at Google Public DNS more) are those which I would never want to go to.

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Update based on your comments on YouTube in other answers.
If YouTube is really banned by your ISP (or higher authorities), changing to another DNS will usually not help (unless this 'ban' is very weakly implemented). You would need to investigate tunneling techniques to bypass such bans.

Try using Namebench to see if it is faster for your location