If you are planning to travel to the Keukenhof on 23 (after 4pm), 24 (all day) 25 (all day) and 26 (before 5am) March 2014 please be aware of the security measures of the nuclear security summit. The exits of motorway A4 are closed, the motorway A5 and A44 will be closed completely. Traffic jams are expected and the government has advised not to travel to this part of the Randstad (between Amsterdam and The Hague) on Monday 24 and Tuesday 25 March unless you absolutely have to. You are advised to work from home or elsewhere. See this link for more information.
The bus between Keukenhof and Schiphol will ride with a detour and will take longer than normal (bring drinks and snacks with you for just in case you end up in a big traffic jam). People are advised to travel by train to and from the airport.
Much better I think is to avoid the airport at these days (severe traffic jams are expected) and take the train from Amsterdam to Haarlem and take bus 50 from there (sorry no combination ticket, buy separate tickets for train, bus and entrance) It takes a bit longer but you might avoid the expected traffic jams on these days by doing this. Use the public transportation site for planning your route because bus 50 is not stopping at the Keukenhof but a 15 minutes walk away. The website will give you all information about maps (how to walk) costs and timetables.