Adding solder to PCB traces to increase current flow
It does work, but it is hard to model reliably and you should use empirical testing to see how well it works for your boards, process, environment, solder. 

There can be a lot of variance from little things that are hard to predict and measure. For example, are you soldering by hand or running though a wave machine? The resulting solder profile cross sectional area can be off by 50% or more depending on which process you use- and neither of them resemble a half circle :) . 

EEVBlog feauted a video where he tests exactly this question...

EEVblog #317 - PCB Tinning Myth Busting

And a similar video...

Does putting solder on high current PCB tracks help?