As CSS Table is reworking, may I say the fixed header table is mostly wanted. The common way to implement a functional fixed header table now is by synchronizing 2 html tables with scripting, it's ugly and complicated. the best way is by giving a height measure to the tbody element if it can works:
#table tbody { height: 20em; }
Above example illustrate a table with a fixed body view of approximate 20 rows regardless how many rows of data it really loaded.