I've cared for over 100 boas in the last 10 years (most were boas I produced) and I've never had one that was just flat out nasty tempered. In fact, I've only been bitten probably somewhere around 6 or 7 times. Every time was because I did something REALLY stupid. I general I take precautions and don't allow them many chances to bite, even the babies. Not because I'm scared of the bite, but because I don't want them going down that path at all.
I have several boas that will strike the front of the cage when I walk by, but I chalk that up to their INSANE feeding response. They see movement when they're hungry and WHAM, they strike. But, once they realize that there's no food, they're back to normal. FYI, those that do this are my adults. Not my babies and juvies.
Coming from BP's, you've probably heard the phrase "red tail" many many times and think (like most who don't work with boas and even a disturbingly large number who do work with boas) that it applies to BCI. This confusion (which is likely intentional on the part of many) exists because people selling them believe (rightfully so) that calling a BCI a "red tail" will make it sell better/faster/at a higher price - even though it's not actually a "red tail" (nor is the tail actually red).
The term "red tail" only applies to BCC. I just wanted to point that out so that should you decide to purchase a boa, you can ask for, and receive what you actually want.
Pictured is a Guyanese BCC - aka - a "red tail" from Guyana:

*picture taken in December of 2010 when my moss was nice and green
This is what a boa that might be called a "red tail" for marketing purposes looks like:

*picture taken last week in the middle of summer when the moss was STRUGGLING and not so green
The second boa is what most people refer to as a BCI. I don't know with certainty that sometime in the past there wasn't a cross breeding with another subspecies so I don't claim that it is "pure BCI" - but it definitely resembles what most people refer to as BCI. In fact, many would INSTANTLY call this a "Colombian BCI" when in fact, there is some Panamanian blood in the lineage (the most common lines of hypomelanism - or "hypo" - originated from Panama). This boa is the by-product of a morph project and MOST boa morph producers could care less about crossing localities or subspecies (like BCI x BCC) so if they do it, it usually gets lost in the history.
So for the sake of simplicity, you can see BCC vs BCI in my two pictures. One CLEARLY has a red tail. The other does not (even though MANY would market it as such). There are also several other differences - some of which are obvious at various stages of experience with boas.
I produced both of these boas. Neither one has ever bitten me or even struck at me 
A boas long-term temperament is MUCH MORE a product of environment/nurture than it is nature. But, I absolutely acknowledge that there are a few individuals which are not handleable without the risk of getting tagged. But, these are VERY few and far between. Like I said, I've had over 100 and haven't had any like this.
IMO, the two most important aspects for a boa to become tolerant (I think "tame" is a poor word choice when it comes to reptiles) are:
-Suitable housing, and
-An appropriate acclimation period
A new boa should be allowed to acclimate to a new keeper for at LEAST 3 months before being subjected to casual handling. During this time, a once or twice daily check on the boa to make sure that temperatures and water level are okay and to check for a dirty cage is all the interaction they should receive - other than being handled temporarily to move out of the cage so it can be cleaned. After the 3 month period, casual interaction can begin for a few minutes here and there and can increase to your desired level as time progresses. I've acclimated MULTIPLE boas this way including some WC imports with 100% success. In fact, my most "tolerant" (or "tame" if that makes more sense) boa is a WC male that I bought in '09.
All in all, it sounds like quite a bit of misinformation is swirling around the BP community regarding boas if others have been subjected to the same information you have. That's unfortunate since boas really are superior to BP's in every way.
lol KIDDING!
If you like the variety in colors/patterns in BP's, I think you'll love boas! We have just as much to offer when you consider that there are 5 subspecies of boa constrictor easily available which all look different from one another. In fact, there are HIGHLY variable appearances even within a subspecies. For instance, "Shield BCC" look VERY different than "Basin BCC" - but they're both BCC. Another example is that a "Colombian BCI" looks VERY different than a "Hog Island BCI" - but they're both BCI.
If you add in all of the color and pattern mutations, it's easy to see that there's a boa for every taste 
I hope this has dispelled many of the myths you've heard. Good luck!
jb
ps, the NASTIEST snake I've EVER seen was a BP. I saw it in Daytona back in... '07 I believe. Just RELENTLESS striking, biting, musking...
-----
What's written above is purely my opinion. In fact, MOST of what you read on the internet is someone's opinion. Don't take it too seriously 
Jonathan Brady
DeviantConstrictors.com Site received a complete makeover! Check it out!