A little disappointed. My first time using a Mac. MBA i5/512gb/8gb ram.
I literally had it in on my lap editing a website for a few hours and the left side got really warm. Then later I received a message saying the tab I was using was consuming a lot of energy... I only had two tabs open.Does that sound about right?
Other than that I love it. Very responsive and simple.
The warning about a tab consuming a lot of energy is an issue with the website that was loaded in the tab. If you open Activity Monitor and sort by highest running CPU process you will see it probably using 100%+ (each thread on a CPU can will display as 100%, so if you have a quad-core CPU with Hyper Threading, you could potentially have a process using 800% of the CPU which means all cores and threads maxed out).
So the site you were on was either stuck in an infinite loop loading some resource, or is just poorly coded.