I am about to construct a built in book case in a new addition to my house. I have never used MDF before, and would like to know if there are any pitfalls using this stuff for shelves etc.

The biggest pitfall is the stuff will bow over time. It's great for several applications but shelving isn't one of them.

Thanks I appreciate the comment

I did a built in, in my sons bedroom and used Oak a little more expensive but looks great and will not bow as talked of by ballenger, another advantage of oak it should last a lifetime. Good Luck!

You Can Can Give Mdf Rigidity By Running A 1x2 Oak Pine Or Poplar Across The Face Of The Shelf

I have some 1/2" square tubing and could dado a grove in the bottom of the shelf and glass the tube in place where it wouldn't show. What do you guys think about that?

Not so much. How thick is the MDF and how long will your shelf be? Take a piece of that tubing and put it between two saw horses and then put a 40 lbs weight in the center, that deflection is what your shelf can still do.

MDF is 3/4 and the span is 30 inches. Thanks for the advice, I'll try the saw-horse test before I commit the time and effort of actually building a shelf.

just spaning 30" id use a clear pine or poplar 1x2, make sure you glue and nail it with 1 1/4 brads

you can always double up the mdf and make it 1 1/2 thick, this will also help.
as for building cabnits in general we use 3/4 birch or oak and mdf for raised panel doors, but that's when its painted, when staining mdf just want work,

I can see why you'd want to use mdf anyway its almost 1/2 the cost of the other 4x8 sheets.

Thanks Glavine, I like your suggestion. The last time I built cabinets I used Red Oak but when I priced it this time it's priced out of my market. 3/4 MDF is $21.40 a sheet here so if I can make it work it will be great. Unfortunately Pine is over priced and the quality of the wood is terrible.

Both Glavine and Gleighvah are using good approaches. Clear pine isn't too bad if you rip it yourself. I have bought pre-cut 1x2 oak strips at Menards lumber for under $1 per foot. Pricey but you may only need 3 or 4 pieces and they look good.

just use mdf for the skeleton and face frame it with poplar 1x2[/B]

Its important to use a solid wood for the frame so you can mount doors and drawer hardware, mdf doesn't hold screws well

I want to thank everyone that responded to my question, I received many good suggestions and now I'm ready to proceed