Can anyone with knowledge of the Netherlands tell me when the big celebration will be next Apr. 30, which is on a Thursday. Will there be bigger crowds on the day itself, the weekend before or the weekend after? We're trying to avoid Amsterdam on really busy days. Thank you for your help.

Queens Day itself is totally packed - can't see the other days being nearly so hectic

when i was there the city simply shut down - all trams, buses and even trains into and out of Centraal Station were shut down

to me a fantastic time to be in Amsterdam but if you don't like mobs everywhere avoid the actual Queen's Day but i think the other days should be quite normal at least it seems so

Queens Day is April 30th - that is the day the celebrations take place, unless it falls on a Sunday in which case the 29th is celebrated.
Amsterdam will be packed, every town and village has it's own celebrations also.
If you want to get out of Amsterdam then do so early but be prepared for difficulty returning by public transport. if it gets too crowded they close all public transport down.

I felt the same way you do -- I didn't want to deal with the crowds. But, we wound up staying, and we're glad we did. It was a great day. If you are there on Queen's Day and decide to leave the city for the day, at least walk around in the morning when things are calm. Here are some of my photos of the day.
http://travelswithdiane.homestead.com/2007Holland5.html

We went to the 2008 festival. There are music events the evening before, crowds were picking up by then. The weather was a bit chilly and damp, so we didn't roam around much. Leidseplein was very full, had a DJ/ loudspeaker thing going on, people wearing their 'crazy' clothes, including the 'required' orange touches. We did normal sightseeing stuff during that day, didn't seem to be more crowded than usual. We also walked over to Spui around 6-7pm but it was dead. As I recall we didn't feel the crowds until closer to 9pm and later.

The next day, we walked all around Vondelpark, Overtoom, Kinkerstraat area to enjoy the 'sidewalk sales' or 'garage sales' that the residents hold. The families hold forth in the park, kids showing off their talents, moms selling baked goods, and everyone hoping to sell off some household clutter. This went on from early morning until late afternoon.

My favorite celebrations were held on the canals, lots of 'boat parades', people cruising on all manner of boats, floats, rafts, kayaks, whatever - loud music, orange costumes, very very fun. There was a huge music event on the grounds of Museumplein, barracaded and policed by officers on horseback. And more DJ music in several of the squares, vendors selling fries, beer, etc. - general party atmosphere.

You cannot do any sightseeing on Queens Day due to the crowds and site closures. Transportation is limited, and know that QD is not only an 'Amsterdam thing', it is held all over. So if you aren't interested, you should time your visit to anywhere in the Netherlands for a week before or at least a couple days after April 30. Hotels often require a long stay during the festival.

Amsterdam on May 1 looked a total disaster with all the trash everywhere. The Vondelpark was being cleaned during the night and looked 95% pristine by late morning. The rest of the streets around Leidseplein were being cleaned but were still a mess, and it looked like it would take at least that day (and maybe more) to get it cleared up. We left that morning to go on to Alkmaar.

Thank you everyone for all the great advice. We may decide to try it after all!