Bob
Are you talking about a workbench or a building table. For the bench you want something heavy so it won't move arround and tough so it will last forever. Most folks use rock maple for this but it is unfortunatly very expensive.

I think however you are talking about a building table. They are very usefull for dealing with the long flexible light weight materials kayaks are made of. Without one you'll end up doing some work kneeling on the floor and that is just misirable. My building table is 25' long by 2' deep and made of 2 layers of 3/4" ply screwed together. I would use ply instead of MDF because it takes a screw better. Clamps and vices are great but i can't begin to count the number of times I've needed to use screws into the table to apply pressure in just the right place or to hold some oddly shaped piece. Another trick I've found usefull is to have a bag o 2" cubes of soft wood with a pair of 3" screws started into them, whenever i need to laminate a deck beam or even a 7' aka I just trace the pattern on the table and screw the blocks down and laminate right on the table (using wax paper of course)

The last thing I'll say is make the table as long as you can as just like in a kitchen there is never enough work space.

: Previously I've made storage shelves topped with plywood. For building my
: next boat, I'm thinking of building workbenches using some sort of a
: compressed-wood fibreboard product I've seen. (It's a pale yellow color,
: with wood chips visible in the smooth finish.) This material (at 1/2"
: thick) looked strong enough to span the 2' width I'm planning for my
: tables. (It was also cheap, at $10 per 4x8 sheet.) I don't know what MDF
: or OSB are (material? strength? appearance?), so any comments on what I
: should look for or what MDF and OSB are would be appreciated. Perhaps I
: should stick with some good plywood?
: Bob