adding more to Bucky's answer,
Also, as I know All previous tools in previous Visual studio works separated, now those tools are integrated as one tool.
You open VB6 for window app, and open Inter Dev for Web app.
Those are separated. But, In VS.NET all tool are in one tool.
This cause another over head too.
Also, there is .NET Framework that is running and giving more step to run application. This also slow down overall processing.
And considering language issue,
in VB interface design code is hidden and processed by VB tool.
But, in .NET interface code and logic codes are in the same place.
So, whenever you switch over Design view and code view with even slight modification, VS.NET parse the code and regenerates the Design view. The parser is more complecated since it consider interface code and logic code.
And often VS.NET makes mistakes while parsing, when switch over between the two mode it also regenerates code.
YOU will notice VS.NET often drops Event registering code.
Some times it doesn't call Form_Load event handler.. ( since the parsing bug..)
Anyway, VS.NET is big monster pressured the strategy 'Alll in one!'.
So, more complecated, heavier, slower with more bugs.. so far..
But, it's really advanced tool and technology.
Just I want to say it takes time to stablize the new technology.
Current Sofware technology trend doesn't go for faster environment, it goes for more stablized and safer software environment expecting users buy faster computer..^^