What kinds of foolish actions does Swift criticize in Gulliver's Travels?
Swift mocks a number of social and political traditions throughout the text. In Lilliput he decries the idea of voting based on anything BUT issues. (Dancing on a rope is not so different from dancing around issues of relevance in an attempt to look good to the greatest number of people.) Elections in the British world of 1699 were not much different than what we see in the US today, which makes reading Gulliver's Travels in 2009 as current as in 1699.
Swift also criticizes people who have large families without the ability to care for them as he describes education and parenting in Lilliput. As he wrote the book, Ireland was deep in poverty and large families were common. This led to a cycle of poverty and begging (see his essay "A Modest Proposal" in the link below for more evidence.) This, too, is a current issue, with the cycle of poverty still unbroken.
In Brobdingnag Swift vents his frustrations at costly wars and national debt--along with corruption in government offices. Again, Swift's words prove timeless, as apparently, people haven't changed significantly in the last 400 years. Power still corrupts.
Swift also discourses about the place of reason in society, the importance of relationship, patriotism, and the importance of moral virtues. He does this by exaggeration and extreme, which proves to be enlightening.