1) Would you mind abstracting the HTTP-part and also allow people to use HTTP_Request2? With HTTP_Request2 there are curl and socket, extensions 99% of all PHP installs offer. With pecl_http the adoption of your package could be considerably harder.
2) How would you compare HTTP_Oauth to pecl/Oauth? [Just as a disclaimer, I'm very much in favor of a pure PHP implementation vs. just a pecl ext, this is more or less because I'm curios.]