Just from a performance point of view, opening LinkedIn webpage is a traumatic experience. I've rarely seen something so slow & heavy.
It's quite sad because LinkedIn gave birth to a lot of fantastic techs, such as Apache Kafka...
LinkedIn is also buggy in many areas too. Search is wild - search for the same thing twice and get completely different numbers of results. This is good to know, when a job search notification shows 5 results, it's not real. Just click the search button and get 100 the second time for the same search!
But the fact it's an SPA works really well I think. Clicking around within LinkedIn seems much faster than the initial load, and things like open message windows keep their state. I like that. You can still right-click just about everything that looks like it could be a link to open a new tab or save the link. So I think they've done a great job of SPA.
It's a shame it's so buggy that I have to reload it from time to time anyway. LinkedIn is probably the only company where I use a product with so many obvious low-hanging-fruit bugs I'd actually consider working there just for the satisfaction of fixing them.