dd can be used to clone volumes, but it's rather slow and only works if the new & old volumes are exactly the same size. For cloning HFS+ volumes, use Apple's
asr command, or one of its many GUI frontends -- the easiest is probably the "Restore" tab in Disk Utility (just be sure to enable the "Erase destination" option). You'll need to boot from something else (you can't clone the volume you're booted from), but that's easy: Disk Utility is available from the Utilities menu when you're booted from an installer DVD.
Whether the cloned volume will boot the new Mac is a different question. In general, when Apple releases a new model, they make a special build of OS X with the necessary drivers added. Then, next time they release an OS X update, they'll roll those drivers etc into the standard OS. For example, if you were running OS X v10.6.6, you could transfer & boot that OS on anything released before 10.6.6, i.e. anything except the latest iMac models. If you wanted to use it it on one of the latest iMacs, you could either update to v10.6.7 before transferring, or transfer it and then boot from the install DVD that came with the new Mac to update it to the special build of v10.6.6.
Or you could just use the Migration Assistant, as @Journeyman Geek suggested.