Replace them all with gutter screws. You would be wise to replace the existing gutters fasteners that are still in place as well. It happened once, it can happen again to the other gutters you have in place.

Here is a link that might be useful: gutter screws

Just make sure before you reinstall this that the surface it is attached to is intact and solid. Sometimes you can get softening/rotting of the wood in this area, and that could be one reason for the gutter spikes loosening up.

I am hopefully going to get my gutters hung TODAY after I finish a little painting. I found something besides a gutter spike I am going to use. I am going to use K style screw hangers, for your typical 5" gutter. I would think it would give more support to the gutters and also comes with a screw. I found them at a few stores around town, a big box store and a more local store, Fleet Farm.

http://www.guttersupply.com/p-hangers-k-style-quick-screw.gstml

Previous poster is right about the fascia board. My parents had to replace their fascia boards. I think gutters trap debris that facilitates the wood going bad sometimes.

Here is a link that might be useful: hangers w/screw

The gutter screws are just as effective as the k-style straps, and your gutters already have the required holes to clear the spikes.

The old spikes tend to work their way out as the wood swells and shrinks with normal humidity.

The gutter screws have threads that hold much better.

Don't forget to get gutters cleaned out before it's to late!

Hopefully, in the 4 years since the original post, the gutters got cleaned.