I made a thread about a week ago asking why Limewire refused to work, and now I know why. It's not that Plus.net blocks filesharing, it's that it's low priority. I just upgraded my service to 2MB, and when I was reading through the "feature list" of my account, it said that

"With Broadband Plus you can use any type of Internet services you want. In order to ensure we deliver a high level of service, during busy periods we will give priority to services such as web browsing and email and a lower priority to high usage services such as downloading and file sharing."

either my old account didn't block Limewire and was just too busy, or my old account blocked Limewire and this one doesn't, just sets low priority to it! So, if you're on PlusNet just upgrade to "BroadbandPlus", should fix the problem(well, if the service isn't busy)