Well, Ferrari for one. Every team in the paddock has a furtive eye on the red cars after their impressive outright pace in Jerez, and then their race pace in Barcelona.
Mercedes' Toto Wolff says: "Ferrari have taken a step, and the GPS data suggests that their performance is spot on. What we don't know was their fuel levels relative to ours, but they look good."
Lewis Hamilton concurs: "Ferrari are very strong, so it'll be interesting to see how this weekend goes."
"Yes," Felipe Massa smirked at Williams, "we are watching them. For sure they will be very strong here. They've made some decent progress."
Strong was a word that Kimi Raikkonen – who is still welcoming his new son Robin into the world – used in reference not just to his team but also the SF15-T's front end. And Sebastian Vettel looks like a man ready to make a point.
New team boss Maurizio Arrivabene has spoken of being satisfied with two victories this year. "That depends on the form of the others," Vettel acknowledges. "But we've made a step and [are] yet to find out how big. We could see last year a chance to win, not just for Mercedes - so if at points we are in a really strong position, at the start of the season close behind, then maybe there's a chance there."
One question that will begin to be answered today, and more so tomorrow, is just how big a surprise Ferrari might be able to stage.
Who else? Lotus will be better, but how much better remains to be seen at a time of re-organisation. Might Max Verstappen do something super-dramatic as F1's youngest-ever rookie?
There's just a chance that McLaren might do something. Clearly, their testing was a nightmare, but the issues that beset them had many knock-on effects, not least of which was that they couldn't run on full power. So if and when those things are fully resolved, some bigger steps than expected might be seen. After all, we already know from Kevin Magnussen's test experience that the MP4-30 is a lot better than the MP4-29.
The key for the Woking team will be getting mileage, particularly after such a limited testing programme.
"Our aim is to finish and get enough mileage under our belt to sort out niggly problems," Jenson Button says. "It's a case of getting out there and seeing what we have. We haven't had a lot of testing so we haven't done much development work or basic set-up work. I have no aim in terms of position.
"We want to win races, scraping into the points in Melbourne doesn't interest us.
"It's the future which is interesting and the important thing for us is to see big gains throughout the year."
Watch out too for Marussia. Their surprise was getting here in the first place; now they are set on making a valid effort to get their updated 2014 cars onto the grid for the opening race of the new season.