It's very easy to use, and can find information without having to look around and fiddle with command line tools. For example, if you type 126.96.36.199 into the whois box, it responds with clickable links to two other blocks, with
Location: United States [City: Bethesda, Maryland]
NOTE: More information appears to be available at NET-65-173-218-0-1.
at the top of the page.
If you click on NET-65-173-218-0-1, it then takes you to the listing for that record, with another "NOTE: More information appears to be available at MF974-ARIN." Message.
Also, if you type in 188.8.131.52 into the whois box, it returns:
ARIN says that this IP belongs to APNIC; I'm looking it up there.
APNIC says that this IP belongs to KRNIC; I'm looking it up there.
And drops you straight to the record containing the NOC contact details.
All of this makes http://www.dnsstuff.com one of my favourite sites.
The site also offers lots of other DNS related tools, too numerous to mention here, you really must have a look around the site yourself.
For the "experts" among us, the site contains two other pages, http://www.dnsstuff.com/pages/expert.htm – containing things like RADB Routing, CIDR/Netmask Lookup, and the very cool WHAT IS? Where you can enter anything and it will tell you what it is.
There is also the test bed at http://www.dnsstuff.com/pages/testbed.htm
which contains some cool new stuff.