I am new to CS and I don't hear a lot of hackers use asp.net for their web app, aside from hosting costs(win servers), what other disadvantage does ASP.NET has?
There is nothing wrong with ASP.NET. The guys at Microsoft who write the developer tools are second to none. The wide availability of excellent books and the choice of languages makes this option well worth considering. The .NET framework itself is great with all the functionality you might want.
The downside as I see it is what I call the "upgrade treadmill" imposed (I assume) by the MS Marketing types - you will be pushed ever onwards once you start down this road. My corporate customers seem happy with that and we have built some great interactive web sites that scale well but it is a factor that you might like to take into account.
ASP.NET is Windows Forms for the web. It uses the same approach as you'd use to build a desktop app in Visual Studio. Which is good if that's what you want to do (or if that's what your developers already know), but starting from scratch, a natively web solution would be better.
I think hosting cost is the biggest issue, especially if you reach a point where you need to balance load across many servers. There is also the cost ofthe development tools, although I think MS has some programs that allow you to get Visual Studio .NET for free or for minimal cost. Other than that, I think there is just a huge bias against the MS stack in the "hacker" (yes, ironic quotes) community. Having worked with asp.net, django/python and rails, I honestly don't see a huge difference between the three in terms of development productivity, but there is definitely a difference in hosting and software licensing costs. Because of that, I've lately been choosing not to lock myself in to the MS stack for any projects that have the potential to require massive scaling.
Not to mention that the average hacker is usually far better equipped to manage a Unix flavoured server than a Windows server. With small companies who can't afford to have a full time sysadmin on staff, what you know is a powerful motivator. Windows server administration simply isn't the type of thing you pick up while using Windows, while the basics of managing Unixen is something you pick up while using Unix boxes.
I'm sorry but I don't see any difference in learning *nix admin vs Windows admin. If anything I think it's the opposite: Windows admin is much, much easier to learn. Where MS excelled early on was in usability and less-training-required - that was kind of the whole point.
This is how i feel as well. Talking about hosting cost, I believe with current VM technologies and the pace it evolves, it will become a less problem in the future?
Reddit, YCombinator, Digg are all rife with anti-MS folks so, if you follow the idea that, "The world must be like what my experience is" and you only visit those sites (or similar ones), then you would absolutely get the impression that ASP.NET is a bad choice. There are as many if not more "hackers" using ASP.NET than all others except maybe php but those ASP.NET folks typically hang out elsewhere.
ASP.NET and the .NET Framework are free no less, and more reliable than Windows itself. And the Mono project (.NET stack for Unix) is open source.
While ASP.NET in its out-of-the-box form may be a bit daunting at times, since it follows nearly the same development model (viz event wireups, binded controls etc) as with developing software apps. But ASP.NET MVC is an upcoming alternate model that is quite flexible and more appealing for web development.
Having worked with MS tools for over a decade I can easily say that the .NET IDE's have only gotten better, more usable and powerful, whether its Visual Studio Express (free) or SharpDevelop (open source).
The basic tools are free but why get locked into MS with all it all its licensing, proprietary software/platform/toolset, upgrade, and cost issues.
MS does make some very good products (I use and like VS2008) but the core reason most hackers don’t use them is because they don’t want these aforementioned issues. This becomes more evident the more you scale.
It is no coincidence the top performing web-apps produced so far have not been based on MS software.
Unless you have a specific partnership or business model in mind that requires it, I'd say ASP.NET's advantages are not sufficient to offset the disadvantage of being coupled to Microsoft's decision process (both business and technical).
MS Tools & Languages are made with corporations in mind. In other words, ASP.Net is structured so that programmers can be treated like replaceable cogs. There really isn't anything wrong with that, but if you aren't in a "replaceable cog" situation, you can get things done faster in other languages that require less boilerplate code.
The downside as I see it is what I call the "upgrade treadmill" imposed (I assume) by the MS Marketing types - you will be pushed ever onwards once you start down this road. My corporate customers seem happy with that and we have built some great interactive web sites that scale well but it is a factor that you might like to take into account.