My only problem with homeschooling is the fact that homeschooled kids don't get introduced to as many people, which could potentially lead to social problems in the future. However, I have several friends who were homeschooled and turned out great. Like myk97 said, it has to be done right for it to be effective.
Personally, I was home-schooled from 1st through 12th grade. For high-school, I joined the home-school program, Classical Conversations, which is a Christian-based program that I believe provided me with an incredible education. Do I believe home-schooling is a decent education, yes, depending on the way you do it. There are home-schooling families I know whose children wake up at 6:00 am, begin work at 7:00 am, and don't stop until 5:00 pm, with the exception of a half hour lunch. They go above and beyond int their work and their standardized testing scores are mostly above average. In this case, yes, home-schooling is most definitely a decent form of education. However, there are other home-schooling families I know whose children wake up no earlier than noon, work until about 3:00pm, and don't accomplish more than reading the chapter or two of a book and completing a few math problems. In this case, home-schooling is not being done correctly and is thus depriving the kids of a decent education. Bottom line, when home-schooling is "done right", it can go above being just a decent education; it can be incredible.