Depending on the types of cars, theft is a valid concern. HiGear was a car service that rented out luxury cars and had to shut down because they were hit by a criminal ring [1].
Agree that its not a showstopper if you're vigilant, so it's good that they're thinking about it from the outset.
When I worked at Google (2010), this was a major pain point. Your @google.com account is essentially a Google apps account and most people have a personal @gmail.com account. At the time, the best solution was to use multiple browsers or incognito mode.
The flows can definitely be improved and I'd attribute this to it being a hard implementation problem rather than a lack of awareness around what a good flow looks like. Most companies don't even try to support letting you log into multiple accounts at one time. Having multiple domains (google.com, youtube.com, Google Apps domains) makes it even more complex.
It’s worth noting that Facebook was hotter than the sun back in 2008, so for it to continue to recruit from other firms could could have been a reflection of its market position; if you are doing the poaching, why would you disarm?
Facebook was much smaller then, and likely had a lot more to gain from poaching than they had to lose.
Since this shows multiple tweets from a single user, the ordering of the users becomes more important. I think its currently ordered by most recently followed. Some other orderings that might be interesting:
(1) Most recently tweeted
(2) Affinity - order by people I reply/RT the most
(3) List view - view users from a specific list
Also, would be nice if you could click on links in tweets directly.
It sounds like good practice in concise communication.