+++ This bug was initially created as a clone of Bug #971026 +++

The same issue was reported with webob in swift3 plugin
(openstack-swift-plugin-swift3 RPM)

# swift-proxy-server /etc/swift/proxy-server.conf
Traceback (most recent call last):
  File "/usr/bin/swift-proxy-server", line 22, in <module>
    run_wsgi(conf_file, 'proxy-server', default_port=8080, **options)
  File "/usr/lib/python2.6/site-packages/swift/common/wsgi.py", line 119, in run_wsgi
    init_request_processor(conf_file, app_section, *args, **kwargs)
  File "/usr/lib/python2.6/site-packages/swift/common/wsgi.py", line 246, in init_request_processor
    app = loadapp('config:%s' % conf_file, global_conf={'log_name': log_name})
  File "/usr/lib/python2.6/site-packages/PasteDeploy-1.5.0-py2.6.egg/paste/deploy/loadwsgi.py", line 247, in loadapp
    return loadobj(APP, uri, name=name, **kw)
  File "/usr/lib/python2.6/site-packages/PasteDeploy-1.5.0-py2.6.egg/paste/deploy/loadwsgi.py", line 271, in loadobj
    global_conf=global_conf)
  File "/usr/lib/python2.6/site-packages/PasteDeploy-1.5.0-py2.6.egg/paste/deploy/loadwsgi.py", line 296, in loadcontext
    global_conf=global_conf)
  File "/usr/lib/python2.6/site-packages/PasteDeploy-1.5.0-py2.6.egg/paste/deploy/loadwsgi.py", line 320, in _loadconfig
    return loader.get_context(object_type, name, global_conf)
  File "/usr/lib/python2.6/site-packages/PasteDeploy-1.5.0-py2.6.egg/paste/deploy/loadwsgi.py", line 450, in get_context
    global_additions=global_additions)
  File "/usr/lib/python2.6/site-packages/PasteDeploy-1.5.0-py2.6.egg/paste/deploy/loadwsgi.py", line 562, in _pipeline_app_context
    for name in pipeline[:-1]]
  File "/usr/lib/python2.6/site-packages/PasteDeploy-1.5.0-py2.6.egg/paste/deploy/loadwsgi.py", line 454, in get_context
    section)
  File "/usr/lib/python2.6/site-packages/PasteDeploy-1.5.0-py2.6.egg/paste/deploy/loadwsgi.py", line 476, in _context_from_use
    object_type, name=use, global_conf=global_conf)
  File "/usr/lib/python2.6/site-packages/PasteDeploy-1.5.0-py2.6.egg/paste/deploy/loadwsgi.py", line 406, in get_context
    global_conf=global_conf)
  File "/usr/lib/python2.6/site-packages/PasteDeploy-1.5.0-py2.6.egg/paste/deploy/loadwsgi.py", line 296, in loadcontext
    global_conf=global_conf)
  File "/usr/lib/python2.6/site-packages/PasteDeploy-1.5.0-py2.6.egg/paste/deploy/loadwsgi.py", line 328, in _loadegg
    return loader.get_context(object_type, name, global_conf)
  File "/usr/lib/python2.6/site-packages/PasteDeploy-1.5.0-py2.6.egg/paste/deploy/loadwsgi.py", line 620, in get_context
    object_type, name=name)
  File "/usr/lib/python2.6/site-packages/PasteDeploy-1.5.0-py2.6.egg/paste/deploy/loadwsgi.py", line 646, in find_egg_entry_point
    possible.append((entry.load(), protocol, entry.name))
  File "/usr/lib/python2.6/site-packages/pkg_resources.py", line 1948, in load
    entry = __import__(self.module_name, globals(),globals(), ['__name__'])
  File "/usr/lib/python2.6/site-packages/swift3/middleware.py", line 58, in <module>
    from webob import Request, Response
ImportError: No module named webob

RPMs installed:
# rpm -qa openstack-swift* python-webob* python-keystoneclient
openstack-swift-proxy-1.8.0-3.el6ost.noarch
openstack-swift-plugin-swift3-1.0.0-0.20120711git.el6.noarch
python-keystoneclient-0.2.3-4.el6ost.noarch
openstack-swift-1.8.0-3.el6ost.noarch
openstack-swift-container-1.8.0-3.el6ost.noarch
openstack-swift-account-1.8.0-3.el6ost.noarch
openstack-swift-object-1.8.0-3.el6ost.noarch
python-webob1.2-1.2.3-2.2.el6ost.noarch
python-webob1.0-1.0.8-3.el6.noarch


The keystoneclient fix definitely does handle webob 1.2 fine:
# python
Python 2.6.6 (r266:84292, Oct 12 2012, 14:23:48)
[GCC 4.4.6 20120305 (Red Hat 4.4.6-4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import keystoneclient
>>> import webob.dec
>>>

But the problem is with openstack-swift-plugin-swift3. We need to add this to __init__.py:
import os
import sys
import pkg_resources

def replace_dist(requirement):
    try:
        return pkg_resources.require(requirement)
    except pkg_resources.VersionConflict:
        e = sys.exc_info()[1]
        dist=e.args[0]
        req=e.args[1]
        if dist.key == req.key and not dist.location.endswith('.egg'):
            del pkg_resources.working_set.by_key[dist.key]
            # We assume there is no need to adjust sys.path
            # and the associated pkg_resources.working_set.entries
            return pkg_resources.require(requirement)

replace_dist("WebOb >= 1.2")

OR, as proposed by Pete, patch swift3 to use Swift's swob
"swift3 is Swift-only. Just swob the heck out of it, I say."