There are definite pros and cons to having a tall raised bed vegetable garden. In this type of garden, you can import high-quality soil and have greater control over the growing conditions of your plants. In addition, I think raised bed gardens are generally easier to weed and maintain. The major con, however, is the higher start-up costs. Each of my 8' x 4' x 20" beds will cost me about $70 - $80 in building materials and that's not including soil. Times that by 8 or 9 beds and it can get quite expensive. Tall raised bed gardens also require more water, which is why I'll have to seriously consider installing a more efficient drip irrigation system next year.
I also considered using pressure treated wood but in the end decided against it. Though the chemicals used nowadays in the pressure treating process are much less toxic than the ones used a decade or two ago, I figured the 7 to 10 years of life I'll get out of these untreated boards won't have too much impact on my wallet in the long run.
I also installed 1" PVC pipping in the corners and middle of each bed using medal straps at the top and 2 1/2" screws at the bottom. These will allow me to install 3/4" PVC or metal hoops easily to each bed if needed. I can also use them to hold up simple trellises.
Once the beds were installed, I added a thick layer of partially composted grass clippings from this past summer and dried leaves. Not only will these break down during the winter and help feed the plants next year, but they'll also help to cut down on the amount of soil I'll have to add to each bed. (Another reason why fall is a great time to start a garden.) The soil I'm using is from a local company and is a mix of loam, vegetative compost and horse manure.
And here are the finished beds. Two down and many more to go.