March 2015 When to go ? When to Not go?

I would go for 10 days the first week of December!

I'd go as early in March as possible because the spring break crowds will only pick up as the month progresses. And the weather will be cooler, also.

We love WDW in March. I have no experience going on a weekday in March, but plenty of experience with Friday-Sunday. We go at least 2 weekends every March.
1. The weather here is beautiful in March. Low humidity, mid-high 70's, sunny with a very nice breeze. Evenings are usually mid 60's and wonderful. Not too hot and not too cold. T-shirts and shorts during the day and maybe a long sleeved shirt and pants at night.
2. It's cool enough that insects stay away and it's before the rainy season.
3. We have found the weekend before Easter to be very busy. Easter is April 5, 2015. All of the weekends in March are pretty busy though because of all month there is Spring Break, St. Patrick's day and Easter vacation. We have never found any of these weekends any busier than Thanksgiving weekend, which is quite busy. I hate crowds, and I can handle the weekend crowds in March.
4. We love the Flower and Garden Festival. I like it way more than F&W because DH and I find 99% of the food at F&W disgusting. I know we're in the minority on that. The F&G Festival is beautiful. I love Epcot during this time of year and it looks a little sad to me now the rest of the year without all the beautiful flowers and topiaries.

If you go knowing that any week you pick in March will probably be busy I think most people would love WDW in March.

On consideration for March--the crowds should be fairly consistent (and by that I mean medium to heavy) all month, so I would consider trying to overlap part of Food & Garden Festival. Easter is early this year, so you might also be able to catch the Easter Egg display at Grand Floridian. It's not as over the top as the gingerbread houses, but it's still pretty impressive.

Can't really comment on May but we have always found the begining of May to be a nice and quiet time .so long as you miss the first weekend.

Our favorite time to go is towards the end of April and early May. Spring break is mostly over, Easter has passed, the Flower and Garden Festival is still going, and the weather is perfect for us. Sunny and low 80s, usually. The crowds have been very manageable during that time

The only down side is that if you go to Universal, that time frame was always Class Day for the local schools, and there were teens by the bus loads! Not sure if that's changed though since the prices at Universal jumped up.

My last three trips were during Spring Break, so roughly, that was typically around mid-March. Crowded but manageable if you get to the parks early and are able to ride most, if not, all of big ticket attractions before 11 am. Though St Patricks Day, things can get a bit crazy. There are crowds there, particularly on the West Side with Raglan Road and Cookes of Dublin in Downtown Disney nearby. Weather wise, I'd say in general, anticipate at least upper 70s and low 80s for the most part. I think there's only been one time in my past three trips where the weather was in the upper 80s but not 90 degrees. But also, expect a lot of high school seniors in colored shirts. I would know, I was one of them six years ago! Fortunately, my class was well behaved, however, that may not hold true for all. And also, I also remember seeing competition cheerleaders on all three trips so I have to think there's an annual competition in March. I think if you avoid the value resorts where the school groups and cheerleaders stay or request a room away from the pool, then hopefully, it's better sleep.

Our disney moon is March 22nd we are staying for 7 days my family have been in March a lot and its okay, it's not that business crowd calendars are a weird thing cause lets be honest WDW is always busy, the trick is avoiding when it's heaving and my experience is summer and the holidays. The only time I have felt uncomfortable in the park due to crowds was Easter day

Brilliant! The end of April will undoubtedly be much nicer than any time in March. We did hit a nasty heat wave in April one year, but it's Florida. That can just as easily happen in December!