What do you like best?
The breadth of targeting that LinkedIn's self-serve ad portal offers is the best I've seen. With options ranging from job title, to seniority, company size and industry, and user skills, it's been really helpful to us in targeting user personas with sponsored content.
What do you dislike?
I wish their targeting allowed for advanced logic (i.e. "A and (B or C)", rather than just "A and B and C"). This would allow us to expand our audience targeting and reach more prospects.
The retargeting is also bit difficult to set up. It seems like the match rate is lower than AdWords, but it's improved a lot.
Recommendations to others considering the product
I would strongly recommend using LinkedIn's marketing tools to anyone looking to generate qualified leads at a B2B organization.
What business problems are you solving with the product? What benefits have you realized?
We use LinkedIn for lead generation purposes. It's a great source of net new leads for us.