PPS: Here is a summary why using Base32 or Base64 encoding in HTTP-style requests/headers.

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From http://groups.yahoo.com/group/the_gdf/message/2442:
- We could choose any encoding, but...
- Base32 is useful for compatibility with URLs and domain names, so...
- We might as well use it in protocol-fields, saving extra conversions and developer inconvenience.
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Which sounds logical... BUT.... at least we could also use Base64 after having a '?' in the location/URN. A HTTP GET could look like this:

Definition: GET /get/hash?[URN] HTTP/1.0
Base32: GET /get/hash?sha1:BCMD5DIPKJJTG2GHI2AZ9HG7HZUN5ZPH HTTP/1.0
Base64: GET /get/hash?sha1:/9n6YmKqNRmcLIiKC+2xRccm68 HTTP/1.0

Right now I prefer Base64 for HTTP encoding (it's smaller then Base32), binary encoding inside binary Gnutella binary messages and a smaller hash than SHA1.