I know what you mean. It kind of worries me when I first put it on Daisy every month. I usually put it on her at night right before she goes into her crate, to minimize our exposure to it when it's at its wettest. That way, too, she's not laying on the couch and getting it on things. I especially try to have the kids not pet her on her back for the next day or two after I've put it on Daisy. I read somewhere that it is not good to expose kids to it during the first 2 hours after application, so I figure if I put it on her right before bed, it'll be at least 8 hours before the kids are around her.
I've had to move up to the 22+ pound size for her now and it seems like a lot of product. I usually give her a bath as soon as it's allowable after putting it on her (2 days). After about the 2nd day the oily spot is all spread out and after brushing her, it's not noticeable at all, even before she's had a bath. And once she's had a bath, there's absolutely no sign of it any more.
Although I'm not 100% comfortable with it, I really feel like I have no choice. We live in Tennessee and fleas and ticks are rampant because it doesn't get that cold for very long in the winter, so I would worry about fleas all year if I didn't use it. I'm hoping if I always use it on her, I'll never have fleas in the house, and if I'm lucky, not even in our yard. So far, so good. The only fleas she's ever gotten were when we took her on trips with us. And the Frontline Plus seemed to handle them after about a day.
So, to answer your question -- I don't really like it that much, but I do think it's been effective for us, so I plan to continue using it. I know Illinois is starting to have lots of Lyme disease now from deer ticks, so I would worry that she might bring ticks in the house. The reason I am familiar with Lyme disease and Illinois is because when my daughter was about 9 months old, we were traveling from Ohio to Iowa, so of course we went right through Illinois on I-80. We stopped at a rest stop and I put a blanket down and was holding my daughter on my lap while my husband played with our 2 year old son on the swings. I looked down and saw these tiny reddish bugs all over my daughter! I freaked out and took all her clothes off and wiped her down with baby wipes, trying desperately to get them all off of her. I took her to the doctor the next morning and showed them some of the bugs that I had saved in a Ziploc bag with her clothes. Two of them that I had missed had attached to her scalp overnight. The next day, I had the Iowa State University entymology department look at the bugs (I worked at ISU at the time). Sure enough, they were deer tick larvae, and so we treated my daughter for Lyme disease. I had apparently put the blanket right down on top of a huge nest of them! Now I'm even more freaked out by ticks than I was before! So I guess I've decided on what I consider the lesser of 2 evils. But I'm not 100% comfortable with it.