I'd say you should never skip such letters unless that's the actual name of the website/company/product/etc.
Going by your example I would understand that papereview.com would be something like paper-e-view - something related to digital viewing of papers. Or Pape-review - a website that reviews Papes (whatever that might be). But you want it to be about reviewing papers so it probably could be misleading if you removed that "repeating" letter. Also this might bring more confusion to visitors as instead of writing two full words, they must explicitly remember that one letter must be removed. The same would be when you create a domain with extra letters like Arrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrg.com. So who will actually do the counting of those letters and remember it each time they want to visit the site?
What you could do is prevent such "repeats" (if the situation allows) like changing paperreview.com to something like ireviewpapers.com (depending on what your website is actually about).
Also, SEO might be actually in your favor if you use separate dictionary words instead of making some abomination. Blogging-platform.com would perform better than tumblr.com as it has a searchable phrase in it's domain name by default (though my SEO knowledge is rusty).