I was trying to get eclipse to install an update and it just wouldn't do it. Specifically the m2eclipse plugin. I kept getting errors about being unable to fix a dependency.
"maven eclipse can not find a solution 3.4.2.M20090204-0800"
Turns out several things help. 1) turn on every site as an available update site, 2) refresh everything, 3) starting at the bottom of the resolve dialogue begin unchecking items one at a time until the error goes away (yeah, obvious), 4) starting at the bottom again, turn things back on to ensure you get everything you need.