Hi all,

Can anyone tell me the drawbacks of ucing SQL Server Express database server as the backbone server in a DNN based project in a production environment ?..........

Ofcause there are its own limitaions of using SQL Server Express, like the limited storage capacity and so on.

But is there any specific pitfalls of using it related to DNN....?

Ofcause if there's not much limitations we simply can use SQL Server Express for small client based projects.......... 

After a quick google check this
and this

The main limitation appears to be: "Perhaps the biggest limitation is that Express only scales to several dozen users, at which point Microsoft recommends upgrading to SQL Server Standard Edition. That said, you could support up to 1000 users as long as they did not place too much load on the database. What Express does not include when compared to SQL Server SE and above is Analysis Services, Reporting Services, Data Transformation Services, and Notification Services but some users would argue that these features are crippleware anyway."

I don't know how much of a load DNN puts on the database, but lets say it's pretty large, can you get away with only giving a few dozen users access to the site? - If the sites are for clients I wouldn't risk it, I personally would want to make sure that their sites are always online to minimise support headaches in the future.