I regularly make Daguerreotypes and teach workshops at CAP in NYC.
There are two alternatives to using hot mercury. The "Cold Mercury" method uses mercury at room temperature in a vacuum. It was developed in the 1980s or 90s by John Hurlock. The other method is the Becquerel, mentioned in a few 19th century texts, which uses a red or orange light to develop the plate. Lots of details at http://www.cdags.org/ or a brief summary of my Becquerrel process here: http://www.alternativephotography.co...-daguerreotype
And yes, it is a painfully difficult, expensive, and unpredictable process, but the results are worth it...