It occurred to me that Ignatios Souvatzis wrote in gmane.os.netbsd.devel.kernel:
>> If you want to have useful roaming support, I think you'd need to have a
>> background daemon connecting to whatever network it "knows". I kind of like
>> that feature from (excusez-moi le mot) Windows XP. 
>
> Recently, somebody (I think Steven Bellovin) has posted a recipe on
> how to configure dhclient to do this.

IIRC he posted an 'It would be cool if we could make it work this way..' thing
which sparked off that project idea for last year's SoC :)

See 

http://mail-index.netbsd.org/tech-net/2005/06/07/0029.html

I'm not convinced you can build a decent roaming setup merely by using
our current dhclient and a script. I think it requires a little more subtlety;
Steven points this out.