In all honesty, it could be either at this point. Since MyEclipse 5.0GA ships new versions of almost every plugin from the 5.0M2 version using the update site will download a lot of small plugins, which is likely much tougher right now due to the number of connections that will be required than one big download.
As a result, if you’re having trouble with the update site you might just want to download the installer for 5.0GA and then install it on a fresh instance of Eclipse 3.2 (not the one you’re using with 5.0M2). That will give you both a 5.0M2 install and a 5.0GA install when you’re done. Then launch the 5.0GA install and attach it to your existing workspace. Once you’re happy with the results, you can uninstall 5.0M2 when convenient.