Purell is 62% ethanol. Back when I used to work in an infectious disease lab, we sanitized our lab benches with 70% ethanol. We sprayed our latex gloves with it before doing experiments that required sterility. Without having done an actual scientific lab experiment with Purell, I’m guessing that it works reasonably well.
What’s the problem with it then? Well, aside from reports of children getting near fatal alcohol poisoning from consuming globs of it, I wonder if it’s too habit-forming. Washing your hands with soap and water is important not only for getting rid of germs, but also for washing away other toxic products and chemicals you may come in contact with. Purell may kill the germs, but the dirt (and who-knows-what-else) stays. If we get in the habit of thinking that Purell (or other alcohol-based solutions or wipes) can replace hand-washing, we might forget about all the other nasty stuff our hands come in contact with on a daily basis.
Final thought: Use with moderation, but don’t forget the importance of soap and water!