These are HDPE bottles, so leaching shouldn't be a major problem. I'd definitely give them a good cleaning out every once in a while.
Personally, I keep a couple dozen of them around, and keep several filled for easy changeout. After use I clean them out with alcohol (soap and water are just hard to get down in there, no brush that small!). I give them a soak, let 'em dry out and refill them.
Hope that helps!
Adding: I'm no expert in the field, though I would think that constantly depleting the bottle is different than putting liquid in it and leaving it for a year. I wouldn't want to use them for long term storage, but for our purposes I don't think it would be a problem. Now if it was LDPE, that might be a different story...
HDPE is used as a "chemical resistant barrier" in many applications, including to protect ground-soil and water supplies under landfills. Still, not sure I'd want to leave liquid in one for a long time.
FWIW, this is the same plastic used in most bottles liquid is shipped in, so unless you order from one of the few companies using glass, or you move your liquid to glass when you receive it, it's really no different.