Really, only two things:
1. Why is Twitter considered "hard to use" by casual users? I just don't get it. You create an account, pick people to follow, enjoy the unending stream of links and banter. Apparently this is hard for people who are used to Facebook: recency is confusing to casual users, while just the thing for, well, people like me.
2. Why isn't Twitter just charging users? It's a hugely important and valuable tool for journalists, activists, etc. I'd pay up to $15/mo to use Twitter. With more than 300 million users, if Twitter could get 100 million of them to pay $1 to $5/month, I see a nice revenue stream that isn't dependent on ads or growth.
Here's Timothy B. Lee's excellent Vox piece on the company.
No, Twitter probably should not be acquired by Google. Take a look at the history of Google acquisitions to see what happens to such companies.