I used Thompson's Water Seal for four years in a row -- using a sprayer. It caused water to bead up just great. What I found though, was that a gummy Thompson's residue built up on the wood that rubbed off on clothing.
These past four years I have left off treatments of any kind. While water doesn't bead up any more, the dock seems to be doing just fine. The gumminess can still be detected.
Perhaps a treatment every third season is the answer.
