No More Multitasking

I've come the the realization that I cannot multitask anymore.  I realize numerous studies have shown that you're not really more effective when you multitask, but I still continued to try.  If I have to sit on a two hour conference call, shouldn't I be able to answer emails, write blog posts and shop online as well?
The problem is my memory isn't very good when I multitask.  Unless I'm truly focusing on something, I forget that I've done it.  There are lots of examples.  I keep putting the same entry in the checkbook multiple times.  It seems that I put in the entry when we spend the money and when it clears the account.  I cannot count the number of times I've gotten in the van and then gotten out to make sure I've really locked the front door. 
There will still be some multitasking.  I'll make dinner and listen to the girls practice piano for example.  Maybe I'll still answer emails while I'm on conference calls.  It's just that for important things, I need to start concentrating.  I think it's one more sign of my old age catching up with me.