Should I build for Silverlight 3 or Silverlight 4?

I have a zip library (DotNetZip); currently the silverlight build is "unofficial" but I'm making it official.

Should I build for SL3开发者_JS百科 or SL4 or both?

Thanks for the input.

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If you are releasing to the general public, consider releasing for both 3 and 4 (and 5 in a few months).

We still have to develop for Silverlight 3, for several clients, as their servers have not been updated to .Net 4 (required for some of the cooler server-side features of SL 4). Plesk based .Net hosting services also do not yet support .Net 4.