Several most popular technical problems with "Add URL" button were fixed. Relevant video: This is an uphill battle, but if you have problems with some URLs — please report, we'll try to find a way.
<meta property="og:image" content="..."> pointing to non-existing images; ‎· псы в рапиде
image hosting services returning 503 with image content ‎· псы в рапиде
Content-Type: <empty> (this one isn't fixed) ‎· псы в рапиде
normal-looking HTML pages that actually return HTTP 500 Server Error ‎· псы в рапиде
TODO: special handling for wikipedia, which is surprisingly uncooperative; workaround for ‎· псы в рапиде