1) why boil the storage jars in water instead of just rinsing in Starsan?
Either sanitation method will work, but I prefer Iodophor to Starsan. Contrary to what a lot of amateur brewers believe, boiling does not render anything sterile. Water make the phase change from liquid to gas (boils) at 212F at seal level. That is not hot enough to kill spores. Spores are not killed until a temperature of 121C/250F is reached. Suppressing the phase change from liquid to gas until a temperature of 250F has been reached requires boiling at 15psi above normal atmospheric pressure. The process is known as autoclaving and it can be accomplished with any pressure cooker that is capable of boiling under 15psi above normal atmospheric pressure (most modern European and many modern American pressure cookers can only reach 13psi or less).
2) after the slurry is poured into a jar from the fermenter, and left to separate, which portion do you want to reclaim? The slurry on top of the trub, or the trub on the bottom of the jar?
If you leave at least a pint of beer behind, you can swirl the contents of the fermenter back into suspension, wait a few minutes for the break, dead cells, and any hop material that made its way into your fermenter to settle before decanting only the liquid fraction, which will be mostly clean yeast.
3) how many times should the #2 separation step be done?
Never, and I do mean never wash yeast with boiled water. It is a bad practice that is not based on science. Always, and I do mean always store a yeast crop under the beer from which it was harvested. Why? Because a yeast culture shuts down competitors by first consuming all of the oxygen in batch of wort, shutting down aerobic competitors. It then lowers the pH to around 4, shutting down pH sensitive competitors like the pathogen Clostridium botulinum, which stops replicating below pH 4.6. Finally, it produces ethanol, which is toxic to all living creatures at different levels, even human beings. Replacing green beer with water results in a rise in pH and the removal of ethanol, both which protect the culture in storage. Washing yeast is one of the worse practices in amateur brewing. I can assure you that professional brewers do not wash yeast crops. Small to medium-size craft breweries usually just pump cropped yeast from fermentation vessels into sanitized soda kegs for storage.
4) I read something the other day that dry yeast (Safale, etc) can't be harvested effectively. Can someone explain why this is?
That is brewing dogma from the days when dry brewers yeast was a hit or miss affair with respect to viability and contamination. I started to brew in early 1993. Modern brewers have no idea as to how bad dry yeast was at that point in time.
5) when brewing another batch using harvested yeast, do you re-harvest the stuff you've re-used ?
It is known as serial repitching and it is how we obtained the cultures used in brewing today. Back when most brewing cultures were not single strain, brewers used to crop and repitch yeast from good batches while discarding yeast from bad batches. This practice is known as placing selective pressure on a culture. Over a period of hundreds of years, these mixed cultures became domesticated and somewhat stable. Brewers used to mostly top-crop yeast. The reason being is that wild yeast and bacteria generally do not rise to the top and form a skin after flocculation is no longer inhibited by mannose, glucose, sucrose, maltose, and the sugars that a yeast culture can reduce to one of these sugars.
6) anyone ever dry their harvested yeast? Seems like a handy way to store it. There's a nice podcast on this site about doing it just wondering what some pitfalls are with it besides tying up the oven for 2 days.
It is a practice that I would not recommend because it ensures that your culture will not remain a single strain culture. The drying process is what used to be large part of the problem with contamination in dry brewers yeast.
7) can harvested yeast be stored in the freezer (slurry or dried) or will this mess it up?
Yes, but it requires the use of glycerol and a non-frost-free freezer.
I started maintaining a yeast bank on agar slants in 1993 because dry yeast was unusable and liquid yeast was only available on the East Coast during the cool months. At that point in time, Wyeast was the only real player in the liquid yeast market and their culture collection only contained about a dozen cultures. White Labs did not appear in the market until 1995. Plating and slanting cultures allowed me to brew what I wanted to brew without having to worry about obtaining clean yeast cultures. Today, the only reason I see for keeping a person yeast bank on agar slants is out of curiosity or for cultures that are difficult to obtain. With good sanitation, if stored under the beer from which they were harvested, most crops will contain viable cells for at least six months in refrigerated storage. If yeast is pitched within a month of being cropped, it can usually be repitched after the liquid portion has been discarded without making a starter. Many of us have restarted crops that were over a year old.