I use one. For me the most valuable aspect of DriveHUD (the program that i use) is that it creates a database of the hands that you play which allows you to replay and analyze every hand that you want and see if you played correctly or not. The HUD part itself is also useful in some tough spots when the situation is 50/50 and statistics that HUD shows can help you take correct decision. Keep in mind though that hud information is just a tool - if you don't know how to use the tool it can make more harm than good.
At the moment I do not use any help program, everything goes in my head as if I were playing live, I do not agree with the use of said help, but hey you have to adapt, changes happen, and maybe in a future resort to them so as not to give too much advantage.
I like the HUD that everyone sees at GGPoker. Tells you at a glance how many hands everybody is playing (VPIP). That's perhaps the most important stat for Zoom/Rush & Cash games. It also gives an indication of how well each player is doing, but that's a little less useful.
He did not use that help system to play, but I think that we are in a certain way at a disadvantage for those who use it, because when we are already regular players of a level we frequent more with the other regulars that we have faced on many occasions and they already have a lot information about our game and movements in their help programs.