Back to original question, I think it would be nice if there is a way to install apps from local. The situation is like this: After I install 100 apps, I flash a new firmware, but I don't want to repeat 100 times waiting for downloading and installing. Is there anyway to install all apps in a folder at the same time. Thanks.

If you perform a backup and restore it after reflashing, it (Application Manager) should allow you to reinstall all the apps you had when you did the backup. I've not actually tried this with the N900, but that is my expectation.

How about install new apps?
Would you let your phone download 1GB offline Navigation apps and install? Some dictionaries are more than 400MBs, how can we wait for that long?
I wish Nokia PC Suite has some functions like iTune in which we can download apps in Nokia PC Suite and sync with N900 so that we don't have to wait for downloading, and we can install many apps at the same time; we can also download apps from somewhere else, paste to NPS and sync with N900.