I'm sorry that it has taken a few days to respond.
I have done some checks on your server. This is the response from Youtube when your server tries to access information from their site:
HTTP/1.1 303 See Other
Date: Fri, 04 Jun 2010 15:38:51 GMT
Server: wiseguy/0.6.2
Location: www.youtube.com/das_captcha?next=http%3A...ch%3Fv%3D7ABJ74_9YyE
X-Content-Type-Options: nosniff
Set-Cookie: use_hitbox=72c46ff6cbcdb7c5585c36411b6b334edAEAAAAw; path=/; domain=.youtube.com
Set-Cookie: VISITOR_INFO1_LIVE=THecVe3eBpU; path=/; domain=.youtube.com; expires=Sun, 30-Jan-2011 15:38:51 GMT
Set-Cookie: GEO=acb75ee21be9aa32960ee74bba85a1b0cwsAAAAzVVPQNagOTAkeCw==; path=/; domain=.youtube.com
Expires: Tue, 27 Apr 1971 19:44:06 EST
Content-Length: 0
X-YouTube-MID: iRl9HaTJOOXUtMkcyOE1yVHRtRHdwU3p5WHJKR3BWTVpkNHh0dWhHVGw4UVVJOVpRdWxKOVN3
Cache-Control: no-cache
Content-Type: text/html; charset=utf-8
Notice the important header:
Location: www.youtube.com/das_captcha?next=http%3A...ch%3Fv%3D7ABJ74_9YyE
From this, I can tell you that your server is making so many requests to Youtube, that the Youtube server is requesting captcha information (which obviously can not be given by the server). This is the reason why your Youtube imports are failing to get the video information. Our Youtube plugin actually uses the Youtube API and so this shouldn't really be happening. However, when the Youtube data is requested, the CURL request just times out without any information being given.
In this situation, this is the text given by Youtube.com:
Sorry for the interruption. We have been receiving a large volume of requests from your network. To continue with your YouTube experience, please enter the verification code below.
As you said, (and I have verified) that videos from other websites are added fine. It is only Youtube videos that are failing. This tells us that CURL is working correctly, and the method used in the hwdVideoShare plugins is fine. However, Youtube is simply blocking access from your server IP.
Who is your Host? Are you on a shared server? It is worth asking them about this, and seeing if they offer a solution (such as changing your server IP).