koan - 12:28 am on Nov 10, 2011 (gmt 0)

Unless it is justified (there are some situations where you might lose data that may require it), it's a spammy tactic and I consider any web site using this to be scammers. Now some web site that can be a bit of corporate kindergardens for many newbies (ex: Facebook, Amazon, etc) also use something similar on external links to remind people that they are venturing in the wild, and I can almost understand it to some degree if they always end up with complaints by confused visitors unrelated to their web properties, but it is still a bit of an aggressive tactic.