After SharePoint 2007 to 2010 for almost a year and some users reported an issue that incoming e-mail does not start workflow on "create item". After digging into the issue, we have identified that this is the same issue is happening on 2010 version.
Since our upgraded was done using DB detach and attached approach, we have the new 2010 farm with all default settings. We were under impression that the previous issue reported that the email processing is running in the context of "System Account", SharePoint declarative workflow cannot be triggered by the system account should be resolved.
It turns out this issue still exists on 2010 RTM version for any declarative workflow. An example is any workflow created using SharePoint Designer.You still need to follow the following solution published here to enable SharePoint workflow for email enabled list.
Run “stsadm -o setproperty -pn declarativeworkflowautostartonemailenabled -pv true” on SharePoint 2010 even you have run on 2007.
You could run the command "stsadm -o getproperty -pn declarativeworkflowautostartonemailenabled" first to verify the property value.
This is just one command we have missed during the SharePoint 2010 upgrade. Hope you remember this.