I really liked the simplicity and design of the Ads Platform in Twitter.
You can visit it here- https://ads.twitter.com
You pay only if the tweet gets an activity (retweet,favourite,reply,follow) or if you get a new follower.
That is an innovative breakthrough in social networks marketing.
Now if only Google Plus and LinkedIn network showed more such options- I would love to promote my blog on Google Plus- but I am not sure on the options.
I also like the simple design that Twitter Ads offers. I do think an initial free $5 for some accounts should help kickstart this adaptation in a much bigger way. The recommended keywords is designed very nicely and subtly. You can click on screenshots for a better look (links have been updated)
Once you finalize your campaign- you should see a campaign dashboard.
You can also click on the Analytics tab on the top of campaign dashboard and see your own activity, thus adding to social media analytics options. Here it is more of a series of screenshots that is supposed to act as a mini- tutorial to make you familiar with the paltform.