Port wine stain or not?

My baby was born with a fairly large purple/pink birthmark on her thigh/knee.  I didn't think anything of it until we saw a pediatrician when she was 2 months old who seemed alarmed and said that we'd have to keep an eye on it because it might get thick/bumpy/darker or lead that leg to grow larger/longer than the other leg.
I, of course, panicked and called the doctor who cared for her in the hospital.. who told me that he didn't think it was anything to worry about.  
Since then, we've seen several different pediatricians (all part of the same "group") who have all treated the birthmark differently.  Some don't seem concerned at all.. they say it looks like a salmon patch and will probably fade.  Others seem to think it's a port wine stain and needs to be watched.

Now OF COURSE we're going to keep "watching" it and seeing the doctor regularly.. I'm just trying to make up my own mind on the subject and decide whether or not it's worth a lot of $$ and hassle to see a pediatric dermatologist to make sure that they don't think that it needs to be treated early or anything.

I've read all of the info I can get my hands on about port wine stains and other vascular birthmarks.. and it has left me with a few questions..
How long does it usually take for a port wine stain to darken?  resources all just say "as the child matures" and I'd love to know if there's any cut-off point where I can begin to worry less.. My girl is 7 months old now and the mark is about the same, if not slightly lighter.  It fades when you push on it.  It has been growing proportionately with her body.  My husband insists that it has actually gotten lighter and that when she was little it was more "red" colored.  

I would love to get any reassurance that it's unlikely to be a crippling birthmark that's going to be thick and bleed spontaneously and cause one of my girl's legs to be gigantic.  Or at least to know if there will ever be a point in time when I can know whether or not this will be the case.  From my reading, it sounds like I might just have to wait until my daughter is 30 years old or so to find out how bad it's going to get!.. and if that's really how it is... I guess I'll have to live with that... but if anyone has any experience with these birthmarks and can tell me anything that might help, I'd really appreciate it!  

Also, I haven't been able to find anything about it even being possible for a vascular stain other than a port wine stain (such as a salmon patch) occuring anywhere on the body other than the head/neck.. which amplifies my fear that this is going to be a port wine stain and lead to all kinds of scary problems... so if anyone knows for certain whether the placement of the birthmark means that it's definitely a port wine stain and definitely going to get worse instead of better.. that would be helpful to know!

[OBVMommy]

I just wanted to say that my DD has a birthmark on her leg that is very similar toy your DD.  I hope we can get an answer!