The slimy interface that the slimy emails lead you to...
Edit: if you want some concrete things... I can never tell if I'm on my "public" profile page or my profile settings page, or how to get to which one. One of them shows my connections and one doesn't or something, but I for some reason finding them is hard every time. I can also never (on the first try) get to a message someone has sent me, because clicking on the message leads me to the persons profile? or similar. Also I don't want to use messages in the first place, I want email even if it doesn't get LinkedIn ad revenue. I don't need people to vouch for my skills at all, most of them don't even know what low-level skills I use on a daily basis. Leaving a group isn't easy. The grays used all over the interface are pure gray, and feel dull, instead they should have a small amount of blue in them. The stream page has a "People you may know" box twice. I'm not "interested" in any of their ads.
LinkedIn's problems stem from (1) a blatantly confusing interface or (2) a user-hostile, ad-focused monetization strategy.
I think LinkedIn is trying too hard to be more than what it is. It's the professional version of the town church. The town church used to record recording weddings, births and deaths. That's it. LinkedIn should be a record of hirings, leavings, new companies forming and old companies dissolving.
Against the background of that basic information, people should be able to solicit me, freely, to come work for them - but they should be prepared to wait for a response as I'm not going to check in with the 'town church' all that often (unless I'm between gigs or thinking about a new gig).
It might be nice to passively check in on past coworkers to see how their careers are progressing - but that's optional.
I think LinkedIn has a pretty bring future as a business/industry news aggregator which will ride on top of the social platform they've built. Think of it as a BusinessInsider/Forbes/VentureBeat/TechCrunch replacement.
Already you're seeing LinkedIn exclusive editorials by guest writers, and although most of the articles in LinkedIn's feed suck right now, I hope they increase the quality soon (e.g. No more "5 ways to be a successful leader" type articles).
If they can capture quality content and deliver it in the right way then I think that will be successful and fuel more growth in their product and revenues.
I've talked to Reid Hoffman about this, and his answer to what LinkedIn wants to grow up to be is something along the lines of "We've built this social platform which is successful + continues to grow, and that opens up a whole wealth of opportunities to build products/services around it [...]"
I think this is the right path for the company, but what's going to matter is execution. So far they haven't instilled confidence in their execution (What happened to their purchase of Pulse? Their aggregations haven't gotten any better....etc.)
