Because humans have a negativity bias, we like to remember fantastical predictions that didn't pan out, like jetpacks, or hoverboards. But it's worth remembering all the times even the most ridiculous-seeming prognostications turn out to be right.
Printerinks' Isabelle Turner made an incredible chart listing about 35 predictions from sci-fi books (plus Ray Kurzweil's Age of Intelligent Machines) that have come true. The really impressive prognosticator here is John Brunner, whose 1969 novel Stand on Zanzibar correctly called everything from TV on-demand to laser printers to the collapse of Detroit.
We've built some pretty amazing stuff in the past century:
My only addition would be that the actual Hitchhiker's Guide to the Galaxy from the book of the same name, which has a lot of similarities with Wikipedia, as Paul Boutin once argued in Slate.
Hat-tip to Ria Misra at io9.