Hamilton certainly has the chance to stand on his own two feet at Mercedes, but settling into a new environment with different procedures will inevitably lead to some less-than-perfect moments. It will be fascinating to watch.
4. Red Bull target fab four
Vettel has a clear plan for 2013: he wants to join Alain Prost as a four-time world champion and help Red Bull win a fourth straight constructors' crown.
Despite these grand plans, the energy drinks team lacked fizz in preseason testing, leaving predictors of form flummoxed and frustrated.
Vettel's fastest lap in Barcelona was two seconds slower than the quickest overall time set by Nico Rosberg for Mercedes.
But Red Bull rarely show their hand in the winter, disguising lap times with higher fuel loads and wheeling out screens in the pit lane to stop rivals taking a peek at designer Adrian Newey's latest machine. The RB9 is an evolution of the car which has dominated the last three seasons and it has looked lithe and strong on track.
Even if Vettel and teammate Mark Webber start the season off the pace, as they did last year, Red Bull have proved they have the resources to fight back and win both titles -- and will still go into 2013 as the team to beat.
5. Red Bull's rivals
Ferrari, McLaren, Lotus and now Mercedes are all expected to go wheel-to-wheel at the front of the 2013 field.
Ferrari say their car is "200 times better" than the much-criticized 2012 model and, with a new aerodynamic upgrade coming for Australia, Alonso will relish taking the challenge to Vettel over all 19 races.
McLaren and the English team's new de facto No. 1 Jenson Button are not yet 100% happy with the new version of the car which won the last race of 2012 at Interlagos.
The MP4-28 looks fast but inconsistent. There have been teething troubles for the team's risky new design philosophy -- which includes a switch to pull-rod front suspension -- but McLaren are gambling on their new concept bringing big performance gains as the year goes on.
After a breakthrough win in 2012, Lotus will also be in the mix and targeting a place in the top-three teams.
Drivers Kimi Raikkonen and Romain Grosjean showed flashes of pace in testing but they did not complete many laps, which means reliability could still be an issue.
Mercedes completed 12 days of testing with the quickest car, ticking off the second highest amount of miles among the teams, which is an important part of race preparation.
There is still some skepticism over whether Mercedes -- a second off the frontrunners' pace at the end of 2012 -- have made a big leap forward in performance.
But equally there is optimism Hamilton and his old karting teammate Rosberg have a genuinely fast car capable of fighting for race wins.
6. Rookies to watch
There are five new faces on the grid this season -- Esteban Gutierrez (Sauber), Valtteri Bottas (Williams), Giedo van der Garde (Caterham), Jules Bianchi and Max Chilton (both Marussia).
All five have something to prove, but Bottas and Bianchi could announce themselves as real talents.
Williams snapped up Bottas three years ago, and the real racing team reckon they've got a real racer to carry them back to the front of the grid. The Finn, 23, is nicely embedded with the team and should score points quickly.
Bianchi has also had good breeding. The Frenchman has been part of Ferrari's driver academy since 2010 and was a tester for the Italian marque and Force India.
His experience with two quality teams should help him settle in quickly, but points-scoring with Marussia -- which ended last season empty-handed and 11th out of 12 on the grid -- will be difficult.
7. Technical rule changes
The rules governing car design are stable this season, which means most cars will be an evolution of what was on track in 2012.