I often read here about people that stop taking their meds, occasionally not taking or forgetting to take their meds. In general, do any or all of these ADD meds (I'm on Focalin XR) work just any ole time you chose to take them or do they work better by consistently taking them every day?

For example, if I really only need to control the ADD during the week for work, can I take it M-F and then off for the weekend? If I do, is it like starting all over again on Monday?

Unlike other meds, most medications for ADHD work better the less often you take them! It is really recommended to take drug holidays like you said. Taking 2 days off from medication a week, will prevent you from becoming tolerant to the meds (then having to constantly up the dose). And yes, on Monday once you take it, you will most likely see a slightly stronger effect than you did on Friday since you took a 2 day break.

But again, some people take them everyday, and it feels exactly the same no matter how often they take it.

I still recommend taking a break. I usually take Sunday off from my medications, and any other random day I have off where I can just be lazy and don't really need the medication.