A.,
My eight month old just started the same thing. It is totally normal and how long it lasts depends partly on his personality and partly on how you handle it, but it doesn't have to determine how he will be a few years from now.
My oldest started stranger anxiety at age 3 months and it lasted a few months. She wouldn't even go to my husband! I played peek a boo with her a lot to teach object (or people) permanence; just because you can't see it doesn't mean it ceases to exist. I walked out of the room for short periods of time or handed her to people and even left her for short trips. Babies really need to learn that "mommy always comes back." Of course there will be some tears - possibly weeping, wailing and gnashing of baby teeth. :) But I have seen what happens when parents go to great lengths to avoid separation and eventually they have to deal with it, but with a much older child and it is MUCH worse. This is one of those things you want to get over with quickly - the sooner the better.
Then my first outgrew the stage and now she is a big time social butterfly. She knew everyone at school, including the staff, by the second month of kindergarten.
My second was fine being left with anyone in the family, but we had to find situations where he would be left without his sister so he could learn to be independent. His separation anxiety came much later, and the first few months of drop off at the church nursery consisted of peeling him off my leg and letting him cry for a good 15 minutes. Again, he got over it and now loves the independence of going to preschool alone. He won't even let me walk him to the door. He wants to be the big boy and can't wait to ride the bus to kindergarten.
My third was fine as long as a warm body was in the room, so separation anxiety wasn't much of an issue because young children always have to be supervised. He freaked out a few times I left him, but never consistently.
So now, with number four, I will be glad when, hopefully in a few months, she realizes that mommy always comes back, just like everyone else figured out.
I have taught preschool, Sunday School and elementary school and my best advice is to be very happy and smile when you separate and make the goodbyes VERY brief when you leave him. Or you can get him involved in something and walk out the door when he is too busy to notice. I know some experts advise against this because they say it will make the kids paranoid, but my experience has been just the opposite. Parents totally make the situation worse when then fall all over their kids before they leave or come rushing back and rescue them out of the situation. They are trying to help, I am sure, but it just traumatizes them.
Best of luck,
S.