The current discussion about solder fountains has to do with copper dissolution. Broadly, copper dissolution is the weakening of copper traces where a trace and a barrel plating intersect due a loss of the copper into the solder. Longer contact time required by high tin solders for the removal and replacement of components have made this a more pressing issue than in the past when using leaded solders. Assemblers deal with this problem by adding levels of process control. So, the less sophisticated solder pot-like solder fountains have become less attractive than the more complex hot air production solutions.
You can find discussions of this nature on the web.
Repair, Solder fountain * APS Novastar, Model GW-10-HT * VJ Electronix 400ST * Electrovert Solder Fountain Systems * ACE Production Technologies, KISS 100 * Air-Vac PCBRM-12 Solder Fountain/Re-Work Station * Hakko HAK-485-V12 * Wenesco Wave type Rework Stations