"gpg --recv-key" 1.4.3 and 1.4.5 will fail when using Polipo
(http://polipo.sf.net/) as a HTTP proxy (set via http_proxy in the environment),
if GnuPG is built without linking to libcurl (which is the case in Debian and
Ubuntu).
It appears to work fine in 1.4.2.2 as well as when built against libcurl.
C.f. http://sourceforge.net/mailarchive/forum.php?thread_id=31171310&forum_id=36515