BalloonFOs is my new term (I just made it up!) to describe the kind of UFOs people see that are just unresolved bright dots in the sky. This is probably the most common type of UFO seen: something far away, too small to see any actual shape, moving across the sky slowly, flying in formation with other lights, etc. etc.
The latest is a New Years sighting over San Diego. This is pretty interesting footage, but they look like candle balloons to me, an easy-to-make do-it-yourself hot air balloon made out of shopping bags and candles (someone in the comments on that link also said this). In fact that's my second guess; my first is that this was something involving the Navy, since there is a VERY large naval base right there at Coronado in San Diego. But either way, I'm pretty sure there is a more down-to-Earth answer to sightings like this, without invoking aliens.