I had prodromal labor with my last three kids.
#2 I had very mild, but very regular contractions for a couple days, then one night I had an hour and a half of serious contractions - tightening all over and the pulling sensation really low. The next morning, I still had very light (so light I couldn't feel them if I was upright, sitting or walking around), regular cntx coming 7 min apart for an hour, then suddenly, every 3 min for half an hour before I went to the hospital (mainly because I was excited, not because I thought the baby was coming). I was dilated to 4cm and because of the regular cntx, they said I was in labor and I got an epidural.
They broke my water because nothing was happening - duh! I wasn't really in labor! Now I know I could've gone days, or weeks, without having the baby!
#3 I had labor like contractions in boughts, lasting a couple hours once or more a day. That started about 2-3 weeks before my due date. And they were gradually changing my cervix, by the time I went in to be induced, I was 6cm.
#4 I wised up and stayed home, so I wasn't checked as much. At one month before my "due date" I could feel the changes start happening. I had regular contractions, just about daily for a month. At one point, I did get checked because I was curious and I was 4cm. That was at least two weeks before I went into baby producing labor. I don't know what I was at when I woke up in labor "for real" but he was born 3 hours later, and those contractions were actually more spaced out and irregular - like 10 - 15 minutes. They never got any closer than that.
With the last two, there was no difference in the intensity of contractions over those last weeks, compared to the contractions I had when the baby was actually close to being born. That's just the way I labor - in spurts...at the grocery store, driving, visiting friends, etc. Frustrating then, but I've decided I won't be frustrated by them this time (if it happens that way again).