I have a site with various workflows linked with InfoPath forms... Is it possible to have a delegation like thing such that.... another user can perform his task in his username...???
You can do this :)
But it's custom development, you need to store the UserToken of the one you want to impersonate and then use this token to open the site and perform the action you want.
It's not going to be easy, but it's possible
There are some workarounds. For example, add user and substitudes in one SharePoint group and grant items permissions for this group at item added event of event receiver.