As in, if i paste a link in my post, the script should automatically fetch the thread title and convert the link to the format
[url=page link]Fetched Page Title[/url]
You can place a timeout for pages that are slow to respond to prevent hang up at new reply/thread stage. You can also use regex to check and not fetch titles when the user has already entered the link in a proper anchor text context.
Giving it a bit more though, the system will also have to pass the incoming link text through a censor and restrict the anchor text to a few defined characters.
Ahmm i don't think it uses vast resources. Its a feature that exists for ages in vbseo. I run it on my big board and it does not hurt us. Instead it creates much more keyword rich anchor text links and can dramatically help SEO(as most users just paste the link and don't take the trouble to enter the anchor text.)
Even otherwise, its nice to know the context of a link in a post.