Its not a 3 month visa they get......the get admitted 'visa free' (hence the name 'visa waiver') and can stay up to a total of 90 days per visit.
Many people enter multiple times per year on the VWP, especially those on business trips, so someone can definitely enter the US on the VWP more than 2 times. I personally entered 5 times in one year.....my trips were short and so I didnt have a problem. Ive seen accounts of where people have done multiple (exceeding 4) back to back visits where they have stayed the entire 90 days and (luckily) were fine (many people abusing the VWP like this would not be so lucky).
So there is no hard and fast number of visits/total time spent in the US per year figures available as there is none.........this is why (as I stated in my last post) this is considered a HUGE grey area and number of entries on VWP (with previous visit lengths being a big factor) before entry denial will be entirely determined upon the POE officer that a VWP entrant is dealt.
No one on this website will be able to tell you how many visits you can have on VWP per year or how long you can stay for in a year as like I said, there are no such guidelines, and no where is it written down/documented.......however, what people on this forum can do is advise you about lengths of stays/proximity of visits etc that 'could possibly' lead to a denial of entry.