LinkedIn is the best tool I've seen for professional networking - offering a way to present one's work history and expertise, as well as find contacts at other companies through people you know. As one's connections grow, your network similarly grows, exponentially. While it's already the best, I believe there are some new features LinkedIn could introduce to further their lead.
Of late, the site has expanded, adding tools for importing contacts from desktop mail applications and Webmail accounts, expanded into new arenas, including services, and started a forum for questions and answers, with the assumption being a contact's response within your network will have more validity than a stranger.
I believe LinkedIn could get even better through adopting features common with social networking sites, such as knowing:
1. How many times your personal profile has been visited
2. Who has recently visited your personal profile
3. Who has similar profiles to yours
4. Who has similar profiles to your connections
(i.e. "More Like This")
In addition these elements, I believe LinkedIn could extend its "Answers" service into something more along the lines of an RFP submission engine. Within your profile, you could suggest your business type, your availability for inquiries for goods or services, and buyers could directly connect with sellers. LinkedIn could add a new tab to their site, labeled "MarketPlace", which is buyer-driven, instead of seller dominated. Unlike consumer-focused auction sites like eBay or shopping engine databases like Shopzilla, LinkedIn would connect a business service with an individual profile, who presumably could be seen as being so many steps away from you "In Your Network".
As LinkedIn grows in scope, and becomes the default professional-oriented resume/contact information database, the opportunities could be seemingly limitless. With a little tweaking, one could set up dating services based on job occupation and geography. For instance, were I looking, maybe I would want to date a prospect in the field of Marketing or Human Resources in the Technology Field who had more than 10 recommendations from peers. Could happen, although I'd make the "Marketplace" a higher priority...
Do you use LinkedIn? How else could the service improve?
Also, feel free to "Get Connected" or view my profile.