I am in the beginning stages of planning a Machu Piccu trip.  A few questions for those that have been there:
1) What is the best time of year to go?
2) How many days is the minimum it will take?
3) What are the options for getting there (from Cusco) and the time it takes for each option?
4) If we hike the Inca Trail, do we also hike it back (is that 4 days each way)?
Thanks.
		
		
	 
I just got back a few months ago. Feel free to PM me if you have any questions.
1. I went in May, and the weather was nice, but I'm not sure if there's a particularly bad time to avoid. 
One recommendation I'd have is to check out Jetblue's prices for flights. They recently added routes to Lima (by way of Ft. Lauderdale) and the tickets were really cheap when I went. I think they were under $600 RT.
2. Do you mean seeing the entire country, or just MP? I don't think you need to spend more than a day on MP to really get the full experience (although others might disagree). However, getting to MP can be a multi-day process if you want to see other things, which I guess is what question 3 is about.
3. There aren't many options to get to MP. The only way to get there is by taking a bus (or taking a steep 3-mile-ish hike) from the town of Aguas Calientes, which is at the base of the mountain. Aguas Calientes has no roads leading to it (although there are roads within the town, hence the bus to MP), and the only way to get to Aguas Calientes is by taking the train from either Cusco or 
Ollantaytambo. When we went we took the train from Ollantaytambo instead of Cusco, which is about an hour shorter, but we also needed to take a 2-hour car ride from Cusco to Ollantaytambo. We stayed the night in Ollantay because there's some cool stuff there, but there's obviously cool stuff in Cusco as well. Both PeruRail and IncaRail offer train service to Aguas Calientes, so compare prices, but they were pretty much the same when we looked.
4. I didn't hike the Inca Trail, so I'm not sure.
EDIT: When you visit MP, I'd recommend hiking up 
Huayna Picchu, but to do that (and even to get in to MP at all, I think) you need to purchase the tickets from MP's website, which was an absolute mess when we planned our trip.