I have tried converting many projects from vb.net 2005 to vb.net 2008, and not a single one has ever made it. Why do you think they even bothered to include this tool if it is very clearly broken? I mean, it can convert some code okay, but I can never load Design view properly, and it'll almost never compile without error.
Whats the point in putting in a broken tool? I thought Microsoft products were always backwards-compatible? Do they have any requirements before running the wizard?
I've never had any trouble with the conversion wizard, but I mostly use C#.
What specific errors do you get?
Also, do you mean from VB6? If so, here's the answer:
VB6 and VB .Net (any version) are quite different. The VB Upgrade Wizard will try to convert what it can, and show you exactly what still needs work.
Generally projects won't compile because the compiler/language/environment has changed, not because there's anything wrong with the project files.
I typically use vspc to convert project files, but I'm usually converting them from vs2008 to vs2003, which Visual Studio cannot do.
If the conversion tool is actually broken (I've had mixed success using it in the past, with the success rate being inversely proportional to the overall complexity of the project), then one reason to include it anyway is to convince developers to start new projects using the latest version of Visual Studio, and not to start them with an older version and hope that the upgrade process will be seamless.
I'm not saying this is why Microsoft would include a broken conversion wizard, but you never know. If you'd like me to delete this answer, Mr. Ballmer, just let me know.