I'm using InfoPath and SP 2010. I'm using calculated fields which works well, but I wonder if there is a way to copy calculated field value to standard list field when form is submitted ?
Calculated value in Infopath is control, OOTB (out of the box), i.e. just visual container. Controls can be bound or not to data fields (and vice versa, it is possible to have data fields without there visual rendering). OOTB, when you drag'n'drop Calculated value control from ribbon in Infopath Designer (IPD), it
As such, it is impossible to copy (or submit) controls to Sharepoint, only data in data fields. One creates data fields without controls in Fields pane (former Data Source pane in IP 2007) and then can bind or not them to controls.
It is also not clear what you mean under "standard list field"
If you meant under it a sharepoint list then Infopath Sharepoint List Form data fields are directly (and rigidly) linked to its sharepoint list fields.
Update4 (in response to comments): I wanted (but didn't) to reply to your first comment that you probably misunderstood something in my answer. It is better if a person comes to conclusions having poked himself. Then, I had a vague vanity that your happiness will somehow pass through unbroken.
First, do not use calculated value control for your purposes - its data source is expression but not data field. It is data fields that are linked to sharepoint list and possible to submit to it.
Second, if you decided to use Infopath, then try hard to use its OOTB features (behavior) without overriding them, they will be pain in the ass if you override them.