OK, here's a general overview. I am a moly user, have been for almost a decade in just about every type of firearm I own, pistol and rifle. I've purchased commercial molyed bullets and mostly now I moly and wax my own. I have, according to my logs, shot just shy of 10K in everything from 17 to 338. I am not an expert (nor did I stay in a Holliday Inn Express last night) but I do have a large body of personal experience.
Moly can build up in a barrel, but is self limiting LONG before there is any safety issue. Due to the nature of the moly coating, it is almost impossible to get it all out of your barrel once it's been properly "seasoned". Properly "seasoning" a barrel for moly is also a matter of some debate, as well.
Moly
must not be allowed to stay in blued or parkerized barrel for any length of time. It is a hygroscopic material (attracts water) and will cause corrosion in a very short time. This has been proven time and time again all over the web. Don't believe it? Coat some copper washed steel BBs in moly, and let them sit outside in the weather for a day or so. They will begin to rust. This is why most of the "professional trigger puller" web sites shy away from moly, their rifles have to live in the real world out in the weather, and moly will cause problems for them overnight with just a few shots fired. Field conditions being what they are, if moly isn't sealed, removed, or neutralized in short order a true operator would end up dead when his primary weapon fails or deteroriates in vital accuracy due to corrosion.
Moly
should not be allowed to stay in a stainless steel barrel for very long, either. As stated above, it will begin to attack the stainless steel in short order, etching the steel. This has also been proven time and time again all over the web. It will take longer for the moly/water combination to attack a stainless steel barrel, but it will happen. Most of the long range (1K) and varmint users/sites are 50/50 on moly. Their barrels are usually precision stainless steel, and get cleaned and oiled LOTS and LOTS! They will likely never encounter the down side of moly because of their maintenance cycle. Their guns live in the "target" world, and do not get dragged in the dirt (so to speak) the way that a true tactical rifle does. If one fails, it's a simple matter to set it aside for maintenance after the match/shooting session and grab another rifle.
Moly in chrome lined barrels is a mixed bag of results. There is no clear indication if the moly/atmoshperic water mix will etch the chrome or not. To be safe, clean and oil!
Sorry to be so long winded. Moly is a very controversial issue. Like most things, there are no absolutes and it's a true give-and-take material. Only you can decide if it's benefits outweight it's disadvantages in your rifles and in your applications.
I hope that this helped.
Tom