Thanks to NPC Serana, everybody can use 2 (two) followers simultaneously in Skyrim. For example, to have both Serana AND Lydia with you (see picture), do this: Choose Lydia at the beginning. Then, when you meet Serana, do not finish her quest series completely: don't deliver her to her father, just take her with you as long as you want. ^_^ This way I had Serana & Lydia with me from lvl ~20 to ~50 and it was da holy fun ... because we were always wandering as a powerful party of three — plus all our summoned and revived creatures etc.!