In my opinion LinkedIn is one of the best networking platforms on the web.  However, there is still a lot of room for improvement.

I have spent some time thinking about how the LinkedIn service could be improved and have generated a list of five features which would most enhance my experience:

1. Event Management:  As the organizer of events, I would really like LinkedIn to provide robust event planning features (e.g., scheduling, reminders, RSVP, attendance logs, feedback loops).  While these tools are available on other services including social networks, such as Facebook, and other services that exclusively focus on event management, it would be very useful to have these tools integrated into my business social networking platform.  This way if I meet someone at an event, I can find , connect and communicate with them on the social network.
2. Group Landing Pages:  LinkedIn groups don't have meaningful landing pages.  The first page a potential member might see has only a few hundred characters of text and no information about group activity (conversation or dialog).  It would be great if content and widgets could be made available to group members and accessed through a single group page.  This type of feature would be most effective is LinkedIn's platform were opened up.  See some of the groups I started here.
3. Ability to Invite Friends to Groups:  Every time I visit one of my group pages, I think of another person who would benefit from that community.  Unfortunately, there isn't an easy way for me to point another person to that group through the system.  While the group owner should retain permission rights, it would be nice if group members could invite individuals (or even their whole contact list) to join a group that they are in. 
4. IM Client: Facebook has a great instant messaging feature - it would be useful to have one on LinkedIn - enough said on that.
5. Picture Sync With Outlook Contacts:  I sync my outlook contact cards with LinkedIn to keep my contact information up to date.  Since lots of people are adding their pictures to LinkedIn these days, it would be great if those pictures were also pulled into my outlook contacts.  Right now the syncing feature only pulls through name, title, email, phone and address (as provided by the user).