These are tools that are used to get the job done. It shouldn't be a factor in how well the product turns out.
HOWEVER, the use of industrial strength MySQL and other items will give you a boost in not having to chase down the .NET issues.
I've got an online job board built in .Net. The programmer who built the site made some big mistakes and now a lot of the site's functions are flawed.
We've since found a new programmer to build us a new site. A business partner has suggested we build the new site in LAMP. Our new programmer is capable of working with both, but I'm still wondering which one we should go with.
Apart from some basic programming courses I've taken, I'm pretty uneducated when it comes to these sorts of things, so I'd really like to hear what the general concensus is on these two platforms. So far my research hasn't turned up anything conclusive.