should i send my three year old to preschool five days?

All I can tell you is that I do. I'm a mom without a paying job at this time, and having some time to myself -- without my son, tho I love him dearly -- helps keep me sane. He loves his preschool and teacher and is excited to get to go to preschool, so that helps.

I have a 4 yr old and my 2yr old in preschool, they love every minute of it!
they cone home with all their projects and that makes me do happy to see their doing something other than watching tv all day!

I think the answer to this question resides in part to the answer about what you do with him when you are with him. Do you sit and read with him, play with him, take walks with him? Or, like the writer above suggests, is home time sitting and watching TV? If the latter, I would say have him go to school, where he will get some stimulation and good fun. Certainly, a three year old will thrive with other children, if the situation is good. But you don't say if it's all day care or not, or why you are thinking of this. Do you have to go back to work? Is half a day possible? The studies do show that at times little boys in particular may have some problems if they spend more than 20 hours a week in childcare. Have you checked into co-op preschools in your area? These are usually run through community colleges and integrate parents into the program, have a parent education feature, and are a great way to meet other parents of children the same age while also getting some free time.

I think the answer to that depends a lot on your child.

I don't think three year olds need preschool, per say, but I think that for some of them it can be a great benefit. At 3yrs old, my daughter attended preschool 4 days a week for 3.5hrs a day and did wonderfully. It did so much for her self-confidence and she loved playing with the other kids. She learned other things, yes, but nothing that we couldnt' have taught her at home. For her, the social interaction was the main thing. That said, I can't see well enough to drive and my husband works long hours, so taking her to places like play groups, the library, park, etc. were difficult for me, so preschool was a great option. If that hadn't been the case, maybe we'd have waited another year. Who knows?

Is your daughter bored with her current routine? Does she get many opportunities to socialize with other kids her age, and other adults?

I think by that age, most children are able to adapt to preschool and will do well if it's a good program, so there's certainly no harm in trying.

If you're uncertain, give it a shot, and if it doesn't work out, you can always pull her out and try again next year.

If there are brothers and sisters at home or children in the neighborhood to play with, that situation is preferable to the money spent on and the more structured environment in preschool. Three days of preschool is plenty for any three-year-old. Remember, they're going to spend many years in school; no need to overdo it at an early age.
Preschool for three-year-olds should be all about play, with small doses of learning to sit still at circle time and how to walk in a straight line to the bathroom.
Be careful about deciding what will work best for you. We have four children, ages 8 - 19, and when they were younger I sometimes got caught up in what would make Mom's life easier rather than what worked best for them. Believe it or not, a year will go by quickly even if the child is not in preschool or does two days instead of five.

Just had to chime in again with a plug for your own sanity. "What would make Mom's life easier" is equally as important as what "works best" for kids. Make your own well-being a part of the equation, too. A sane parent makes for a sane child.
As to the anti-preschool studies, they have been misconstrued by the news media. There is really no good evidence that a good-quality preschool or daycare is anything but good for kids. What studies have found is that bad daycare hurts kids, but then so does bad parenting. The notion that a mother is the only person who can give her children the care they need, 24/7, is a myth -- part of the "motherhood religion" decried by Judith Warner in her book "Perfect Madness: Motherhood in the Age of Anxiety." It's well worth checking out: http://www.amazon.com/Perfect-Madness-Motherhood-Age-Anxiety/dp/1573223042
Oh, P.S. I interpretted your question to mean "Is it OK/ethical/safe for my child to attend preschool five days a week (so I can get some stuff done/have time to myself/etc.)?" If that's what you meant, my answer is still a wholehearted yes, as long as it's a good preschool.
But if you meant "Does my 3-year-old NEED to attend preschool five days a week (to prepare for kindergarten/life/etc)?" my answer is no, not at all. Preschool, as these other parents said, is mostly about teaching children to socialize. You can get those skills somewhere other than a formal preschool.

This is a very individual decision, but I’ll do my best to give you my perspective. It is very difficult to get the same level of care from someone other than yourself. On the flipside, its very difficult to care for your child on your own all the time and still care for yourself. This article, http://www.babycenter.com/0_stay-at-home-parents-overview_5959.bc, describes one study that determined that children that spend the entire day in daycare experienced more stress and aggression. Another study determine that kids in daycare do better academically and socially. I tend to agree with both studies and believe that you need look at as many preschools as possible to find the one that’s best for your 3 year old. You will find most preschools are listed at http://childcareavenue.com. If you set up appointments and visit each at active times in the day, you will get a feel for how they handle aggression, how the children interact with one another, whether the school is purely daycare or if they are a learning organization, and how the children that are there 5 days per week seem to be emotionally. I think you will find that there is a good fit for your child and it will be good for you too.