I use a password manager utility to store all my usernames and passwords in an encrypted database. From time to time I print them out and deposit the list in a safe deposit box as a backup. Each time I do this, I make a mental note of how many entries I'm keeping track of.
When I started using this password manager about five years ago, the database contained 59 entries. Today it has 254.
To quote a favorite line from a favorite movie, "That's a lot of nuts!"
Admittedly, there's some dead wood in there, and a few are entries I maintain for clients to help them out when their memory fails, but I'd guess easily 80% of what's in there represents my own active accounts of one type or another.
What's amazing is how many of the dumb things I can remember without looking them up. Talk about brain clutter...
No real point to this, just the observation that the list has gotten that large and the speculation that most of us -- software developers, anyway -- probably have to keep track of an equal or greater number. What about you: how many usernames and passwords do you need to keep track of?