What are some good practices when asking people to share their PowerPoint presentations from a conference/talk?

There is no magic when it comes to asking for presentations. And there is nothing wrong with being the person who asks people for their powerpoint slides (at least you show that are interested and it may result in them being cited; and it shows that they got their job done - though a presentation they interested others in their idea).

If they don't reply (or don't sent it), it is usually of one of the following reasons:

• They are busy and missed your mail,
• It would take their time to find the presentation and send it (it may be big so it is not just sending an e-mail),
• They would prefer not to make it public as:
  • It is not polished enough for anything but a presentation,
  • It may contain things that they would prefer not to share publicly (e.g. plots form other papers, preliminary data which may later proven to be wrong or incomplete, pictures or video they don't have right to share further, etc).

If they don't want to share it - they have right to it. However, usually they have nothing against (and actually are happy to do so) as long as you make it quick and easy for them.

So it is a good idea to ask for slides just after their talk - they may have it on their computer (so you can copy it to your stick) or on a stick (o you can copy it to your computer) or send it right away.

Also:

• Send your e-mail at most a week after the presentation,
• Be short and concise (what exactly you want, what do you want with do with it),
• If there is no response try writing the same e-mail a week later.

Be very clear on what you want it for, particularly whether you will be sharing it further (even within your group, with your advisor, &c).

I often post edited version of the slides online, but I always want to have control on the contents that are public, semi-public, or private.

I don't mind sharing my presentations, but I make sure that I provide a read-only format only (PDF) with slides scaled to e.g. 1/4 of actual size, in raster format (so that more than one would fit on a page). When people ask for presentations, I expect they'd like to have the material handy for further reading and reference, not to present it or use it themselves.

One would go even further and restrict the PDF printing, copying and modifications, although these can be circumvented with a reasonable effort if you know what you are doing. I don't do this as a matter of principle, but I can see how some people might want to have such kind of control.