We say it all the time. I'll admit, quite a few of them come from habit, like when he leaves for work we say "I love you" and smooch as he heads out the door. But sometimes, he'll catch me and say it again, just to let me know he still means it.
In my last marriage, it very quickly became routine and lost its meaning. My husband now and I have been together for 3 years and have gone thru just about every hardship and challange you can think of and the words "I love you" have never lost their meaning. We say it alot for no reason thru out the day and he says it just as much as I do. Its really cute. We even have little codes. Like when we can't say it, he'll squeeze my hand and I'll squeeze it back to say "i love you" :)
That's a very good question! I honestly don't keep track and perhaps I should ;) I know we do the usual ILY when we get off the phone. We say it randomly but probably not daily. We've been together 16yrs total. I'm sure we said it daily in the early years.