I did work for a company that tried to do a conversion to .NET.

This software is written in foxpro 6 with foxpro tables. It's a huge app, also about 10 years of changes made by about 12 programmers over time.

There were 2 forces in the company, one wanted a complete rewrite, the other one wanted to put the tables in SQL Server (since the reason for change was that one particular table was getting corrupted all the time, it turned out to be a problem with the backup on the server, found about 2 years later). Well the camp for the entire rewrite won. They put 3 programmers to start rewriting the app, at the same time the developers maintaining the current system (where I was at) kept getting new requests for changes.

After about a month the manager of the other group kept requesting to put a hold on requests (which go on the current system, BUT that meant that the new system also had to have those changes) but we all know that business doesn't work that way, so it was not possible. After about 6 months they probably were 10% (if that, mostly screens without the business logic with is the real time consuming) of the way and not really gaining ground b/c of new changes, so at the end it was scrapped, just to big, it probably would have taken doubling the developers AND good management to actually see real progress, so that team was ousted. The other team did a partial conversion of tables to SQL Server and the app keeps running good (not n-tier, some good code, some ugly code in other parts but works good and mainteinable).

Company lost about 150 grand on that adventure.

Not considering if it's good or bad for business if you guys plan to go for a total conversion think about how many changes you guys do currently, how long it takes to do them and how many people do them. If I'm not incorrect those changes have to also go in your new system.