I have been using Open dns for a long time now and I highly reccomend it. It is very very easy to set up and if you don’t like it or have problems you can just go back to your old dns number.
This may help some peoples connections to speed up and of course it’s FREEEEE. Try it and let me know how it goes,
http://www.opendns.com/
Don’t forget to write down your existing DNS if you want to go back, but I don’t think you will 
From a content filtering perspective it looks good and something I might look into as my kids now use the internet for schoolwork.
How do you find it at blocking unwanted stuff?
As for speeding up a connection, I don’t think it will make any difference to most people as Domain Name Service resolution takes milliseconds and is only done once to resolve the DNS name to IP address. Once this has been done the name is cached within your ISP’s DNS server so no further lookup is needed. If you have a router, this too cache’s the IP address.
I use open DNS and have for quite a while, replacing my ISP settings. My ISP’s DNS tends to be a bit flaky so I needed to use an alternative. Haven’t used the filtering yet and in terms of speed Keets is right, you’d never notice if there was a increase in speed. But at least it finds what i’m looking for
Q. How do you find it at blocking unwanted stuff?
A. First class
As for speeding up a connection, I don’t think it will make any difference to most people as Domain Name Service resolution takes milliseconds and is only done once to resolve the DNS name to IP address. Once this has been done the name is cached within your ISP’s DNS server so no further lookup is needed.
But if your ISP’s cache is crap your connection will struggle. Open the DNS home page it will show you some examples of how and why this can happen.
Don’t forget you can set up Phishing filters, Porn site blocking ( important if you have kids on the PC )
Just give it a try, you can always go back to your ISP’s dns anytime you want. If it’s better then great, if not it’s no biggie you just change it back to your original numbers. Go on be a devil