Have a look in bootnodes.go. It's still 3 for the Geth clients:
// ETH/DEV Go Bootnodes
discover.MustParseNode("enode://a979fb575495b8d6db44f750317d0f4622bf4c2aa3365d6af7c284339968eef29b69ad0dce72a4d8db5ebb4968de0e3bec910127f134779fbcb0cb6d3331163c@52.16.188.185:30303"), // IE
discover.MustParseNode("enode://de471bccee3d042261d52e9bff31458daecc406142b401d4cd848f677479f73104b9fdeb090af9583d3391b7f10cb2ba9e26865dd5fca4fcdc0fb1e3b723c786@54.94.239.50:30303"), // BR
discover.MustParseNode("enode://1118980bf48b0a3640bdba04e0fe78b1add18e1cd99bf22d53daac1fd9972ad650df52176e7c7d89d1114cfef2bc23a2959aa54998a46afcf7d91809f0855082@52.74.57.123:30303"), // SG
I don't know who maintains them - I'd be speculating if I made any suggestions.
If they disappeared then no new nodes would be able to bootstrap into the network.
admin.addPeer()we add nodes to the list of "static" nodes rather than bootnodes. This shouldn't make any real different - it should still work :) – Richard Horrocks Nov 12 '16 at 22:16