It's entirely possible to use Ubuntu or Mandriva (Or plenty of others, but IMHO those are the two easiest) entirely from the GUI, and never go anywhere near the terminal.
To offer a counterpoint from my own experience: at one point I installed Linux Mint, which is about as GUI and user-friendly as it gets. I immediately encountered multiple issues that could not be resolved in the GUI (i.e. within 24 hours). None of the posted solutions on the Mint or Ubuntu forums (Mint is Ubuntu based) worked to solve the issues. I flailed around trying how to's for days. Ultimately, I had to read a book or two before I knew enough to fix those issues, which were created by the pre-configuration options done by the distro and were essentially unique to Ubuntu/Mint, which made general documentation (or Debian documentation) useless. The user-friendly distros do tons of preconfiguration that is designed to help, but can make it much harder to figure out what went wrong when you have an issue.
I spend a lot of time on various linux support forums, and a lot of the questions come from people who don't know what file permissions even are because the GUI hides all of that from them. They pick up terrible, dangerous habits, like just adding "sudo" when a command doesn't work to see if that fixes it (I can't tell you how many times I've seen "I downloaded this random script from the internet, and it threw an error, so I tried running it with sudo").
I've fooled around with a half-dozen distros (including Ubuntu), and I had a miserable experience "just using the GUI". The various Linux GUI tools are just too hit or miss on a lot of basic functionality. I've had to do console configuration for: wireless adapters, hotplugging external hard drives, multiple monitors, 3d graphics card drivers, laptop suspend/hibernation handling, power management, network shares, and I could name a dozen more basic areas which are essentially "plug and play" on Windows or OSX, but the Linux GUI tools left me hanging. To be clear: all the things I mentioned sometimes work out of the box with the GUI tools (depending on hardware and distro), but sometimes they really don't work out of the box with the GUI tools at all.
Don't get me wrong: installing Linux and trying things out is important and necessary. You'll learn a lot by paddling around, and no matter how many books you read, you'll need to read and follow the occasional online how to's because there's so much "stuff" in the Linux world; you'll never learn all of it. But I think it's better if you have some idea of what's happening in general, so you don't just start using sudo as a swiss army knife or reinstalling the OS to undo configuration changes that the GUI lacks the tools to undo.
Everyone has to find their own way though, Linux is definitely all about choice