How does image_lib perform under heavy usage?

[eluser]Derek Allard[/eluser]

Do you think this will impact the performance of the server on concurrent uploads?

Yes.

1) Which configuration(s) should I modify on my server to handle uploads better? (if any)

Uploads probably won't be the (main) problem, it'll be image manipulation once they're up there. For that, probably more ram, and I think GD2 performs faster then the other image libs, but I'd look into that.

2) How do you queue image resizing? and how come many sites (like facebook for example) upload and resize my images immediately? what are they doing differently?

You'll need to build it yourself. Comparing yourself to facebook is a dangerous road to go down, they have resources that you probably don't have access to. That said, if not all 1000 visitors are literally using it at the same time, then I have no reason to believe you couldn't do it on the fly - but you specified that they'd all be using it at the same time.