I live in Los Angeles County, as I have done for the last few years. I moved to a new house about a year ago, still within LA, and several weeks ago I filled out (and mailed) a new voter registration form for my new address.
Today I called the LA County Registrar to make sure I was registered to vote in my new location. Guess what? I'm not. They still have me at my previous address, and have no record of receiving my form. The man with whom I spoke said I should fill out another form, and mail it in again, as they update voter information within 24 hours upon receipt. He had no explanation for what happened to my previous application, and had no assurances that this one would fare differently. I asked about registering online, since they seemed to be having issues with the mail. He said that I could fill out the form online, but I had to print it out because I had to sign the form.
Now, California has online voter registration, which allows you to use your DMV information to sign the registration form electronically. This obviates the need to print out a form, sign it, and then mail it in. But not all states do, and in CA "mail-free" online voter registration was just launched last week, so this guy probably doesn't know about the changes.
The point is, I thought I was registered, and I'm not, and the deadline for registration is getting close. Please register now if you haven't, and double check while there is still time to fix a mistake. As a last resort, a few states (Idaho, Iowa, Maine, Minnesota, Montana, New Hampshire, Wisconsin, Wyoming, Iowa) and Washington DC have Election Day voter registration. California will, but not in time for the presidential election. Connecticut and Rhode Island have Election Day registration for presidential elections only. If you live in one of those areas, please don't rely on this. Register now and you can focus on GOTV between now and Election Day.
People in North Dakota are probably ok, as that state has no voter registration requirement at all. Everyone else, make sure.
Thanks to user mkbk57 for this link (from the comments) to check your registration:
http://www.canivote.org/Also, you can check your state's board of elections, secretary of state, or elections division.
The site seems to work for all states. I just checked for myself, and found out my polling location has changed.