I made a table two years ago.
http://wood.lippman.info/oakdiningroomtable
It is made out of 5/4 red oak. I bought the wood at a liquidation auction at a commercial woodworking shop, so I presume it was kiln dried, and it sat in my basement for 2 years before becoming the table.
It was well jointed and glued up with biscuits. I did a good job of matching grain, and after sanding the joints were very inconspicuous.
Now I can feel the joints in places with my finger tips. It is not much, less than the thickness of a sheet of paper, and only in a few places; if I hadn't made the table I probably wouldn't be aware of it. But I did, and I am.
I have only been woodworking 4 years, but I felt some older projects and they are still perfectly smooth.
Is this normal? Anything to be concerned about it? What could cause it?