I know this question has been asked a million times in various ways by different businesses, but I'm wondering the community's opinion on it [There's this question, but in the fast-moving world of tech, a year is a long time]. For hypotheoretical purposes, let's consider a website where users can watch videos, a la YouTube, Hulu, etc. (actually, it's an on-demand transcoding solution, but close enough). The website could deployed:
<video> tag(Let's assume, again hypoteoretically, that the all-Silverlight version is not as annoying as most all-Flash pages are today, but instead provides an experience similar to a desktop application)
Which way would be able to reach a large percentage of the population? How would people feel about having to install Silverlight to view a site -- how much would they want to see the content to make them click the install button? What if a user is browsing the site at the library on on another public computer with limited bandwidth, possibly using older hardware and with an unprivileged user account -- how easy would it be for them to install the Silverlight runtime?
I really want to use Silverlight since I like its' model (I've been using it for an internal app at work, and I think it's an excellent platform), however I'm afraid that for a public site, a large percentage of users would not be able to view the site, then Flash may be better option.
EDIT:
Well, the idea is to have a player where users can access videos on their home PCs from the web. So the users usually won't be using a home PC -- they'll be using work PCs, friend's PCs, public PCs, etc. That's why I'm worried about the security/install privileges issue.
Start with what each of technologies can do for you and match that against your requirements re: content delivery. Assuming each is just as good as the other for the purpose at hand, and that you have the requisite skills in each or dont mind learning them to produce your content, then dont see player distribution as a problem.
Users not having the priviledges to install the player should it be absent would generally be considered an edge case. If your site is specifically targeting a user group to which this is more likely to apply then obviously it requires deeper consideration but at the end of the day you're always going to have a percentage of surfers who cant do something, or use something, for some reason. In this case it's likely a small percentage and good design dictates some form of graceful degradation regardless of the technology being deployed.
Your other questions re: user preferences is difficult to gauge. Here is a list of sites that clearly dont think its an issue. You'd have to extrapolate the adoption rate numbers but this link, albeit to an MS blog entry, suggests the adoption rate is high, especially considering Silverlights relatively short life.
You also have to factor in that it's an MS technology so you're going to benefit from Windows Update, etc and the strength of the MS marketing machine.
Recommendation: Go for it. The more the merrier.
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Richard