Spoiler Alert: This post includes many details about the gnome starting area in Cataclysm.
As a new gnome in Cataclysm, you begin with the debuff Irradiated. You've been exposed to dangerous levels of radiation and risk being turned into a leper gnome. You are located in the heart of Gnomeregan, surrounded by equipment and other survivors. This is because beginning gnomes in Cataclysm are not the gnomes who've been sleeping on Ironforge's couch for the last half-decade; these are the gnomes who have been surviving in Gnomeregan for years.
The action starts when you talk to Nevin Twistwrench, who warns you there will be more time to talk once you're safely on the surface. Don't worry, though, Nevin has a plan. After all, he is the leader of S.A.F.E., the Survivor Assistance Facilitation Expedition. Your questing starts when he asks you to kill 6 of the attacking leper gnomes because if you are all Pinned Down. As you cut down the marauding lepers, pay attention; you'll hear the awesome ray guns being employed by S.A.F.E operatives.
Once you've helped S.A.F.E. beat back the horde of leper gnomes, you are ordered to Report to Carvo Blastbolt. If you've never been to Gnomeregan before now, this part might seem tricky. As you come out of the room with Nevin, you can choose to make a hard right and go past the barricade. Those stairs will take you to the level where Carvo is blasting bolts. However, this isn't required; despite how the ramp up to Carvo looks, you can actually run straight to him.
No Gnome Left Behind
Carvo realizes that your arrival means Nevin is nearly ready to withdraw from Gnomeregan, but Carvo's a "no gnome left behind" kind of guy. He gives you a teleport beacon to use on your fellow gnomes so that his team can See to the Survivors. The beacon is an object that is placed into your backpack. Run up to the survivors, who are gnomes cowering in fear, and zap them with the beacon. When you hit the cowering gnome, he will disappear away to safety. In the beta, all of the leper gnomes in this area are neutral, which means they won't attack you unless you attack first.
Once you've rescued six survivors, you're told to Withdraw to the Landing Room! You can follow the yellow arrow on your minimap to get to there. If you're familiar with Gnomeregan, the Landing Room is toward entrance of the old entrance. Gaffer Coilspring is standing in the center waiting for you.
Gaffer is fabulous. You can tell by the glasses. Redheads with glasses? Fabulous. She takes one look at you and realizes your irradiated butt needs decontamination badly. She sends you to go through the Decontamination process at the Sanitron 500. It won't hurt ... much. (Note that this walk-through was created on a mage, and this part could be a little different depending on your class.)
Walk over and right-click one of the gyrocopters. As you pass through the room, you are blasted, hosed down with water, and blasted again. Just as everything seems like it's going OK, the copter explodes. Don't worry -- that's part of the gnomish experience. When you talk to Technician Braggle, he congratulates you on your minty-fresh feeling and sends you To the Surface. You talk to Torben Zapblast to get your teleport to the top.
On the surface
After being teleported, you find yourself in New Tinkertown in front of Nevin. He tells you that he considers it a huge victory every time a S.A.F.E. expedition can retrieve survivors. That is how the gnomes are ensuring The Future of Gnomeregan. Nevin then sends you off to find your class trainer.
I want to note that the music in New Tinkertown is exceptionally moving, especially for gnome players who've been loyal to WoW over all these years. It really is an amazing score. My hat is off to the musical team. Not only is this absolutely wonderfully appropriate to the gnomes but it is probably going to be my favorite video game music for a long, long time.
Your class trainer sends you to meet High Tinker Mekkatorque. Mekkatorque has apparently made it his mission to meet every single new gnome escaping Gnomeregan.
When you meet Mekkatorque, he fills you in on what went down during Operation: Gnomeregan. As you watch the holo-table display of those events, the King of Gnomes warns you about Razlo Crushcog. Razlo is a minion of Thermaplugg, and he must be dealt with.
To begin this process, Mekkatorque sends you to Engineer Grindspark. Grindspark is working on a robot to clean up the irradiated airfield, and Grindspark sends you to gather up spare parts for that robot. These parts are sparkling on the ground and shouldn't take long to find. Once you return with the spare parts, Grindspark gifts you with a GS-9x Multi-Bot. After all, this is A Job for the Multi-Bot. Follow the yellow arrow on your minimap to get to the airfield.
You'll be able to pick up a quest from Corporal Fizzwhistle on the way. Since you'll be Dealing with the Fallout anyway, this is a good time to grab it. Destroy the Living Contamination and Fizzwhistle will reward you immediately, without any followup quests.
Sludges with faces
To finish your task for Grindspark, simply walk the Multi-Bot near the geysers to get him started. You can walk in the green stuff, and the enemies here are still neutral. However, you should check out the Toxic Sludge, which has a face and electronic parts attached. It looks pretty neat.
When you've completed the job with the Multi-Bot, return to Grindspark. At this point, you may have a class quest to complete, so keep an eye on your trainer.
You pick up normal questing with Tock Sprysprocket. Remember those Toxic Sludges with the hats? It turns out those nightmarish creatures are the eventual fate of any irradiated gnomes. Those sludges were once people! Tock needs you to go back down to the airfield and retrieve the sludge's belongings. Those hats are all of What's Left Behind.
Along the way back down to the airfield, you can grab a quest from Captain Tread Sparknozzle to find out What's Keeping Jessup? You complete both quests by heading due south from Sparknozzle, stopping at the airfield first. After you've killed the Toxic Sludges and collected the possessions, keep going south and move more west. Watch your minimap for the question mark quest marker. You'll find Jessup McCree hanging out by a tent at the edge of the airfield.
Things haven't been going so well for Jessup. He needs you to Get Me Explosives Back and free his men from their cages. (In dwarven philosophy, being captured means you've gone Missing in Action.) You can do both quests right next to Jessup by killing and looting troggs and opening cages. Return to Jessup once you've completed the quests. In gratitude, he'll immediately send you to the bottom of Frostmane Hold to be Finishin' the Job.