I rarely boot up at the car. Over the years there have been periods when I tried it. I found its acceptability depended on a few variables:
- what the weather is doing
- what the ground surface is like (puddles, mud, gravel? solid and dry? packed snow?)
- is there something to sit on? Like a rear hatch without much of a lip. I find trying to boot up sitting sideways in a seat is horrible: the door doesn't open far enough (especially if there is another car next to you), the seat is trying to make you slid too far into it, etc.
- how many people you have. If the good sitting/leaning spots on the car are fewer than your passengers, you have to take turns and wait.
Nowadays I would only do it in special circumstances, such as it being a long uphill to the lodge and downhill to a lift (and already having a ticket).
One other thing that may affect how people feel about booting up in the car -- whether they need to go inside anyway, for example to buy a ticket, use the bathroom, meet people, or wait for the lifts to open.