I would suggest against sharing your personal AdSense login account information with anybody.

Thanks. That's what I plan to do. Still, my partner should be able to see the daily performance, generate AdSense code and a few basic operations. Don't tell me that AdSense is only used by 1-person companies; surely many big companies use AdSense and more than one employee has access to AdSense login?

If so, those companies still have to comply with AdSense rules. If your partner needs to see daily performance call him/her into the office to look at the screen, or print a bunch of paper and put on his/her desk. Beware the logins by others. Too many horror stories of folks losing their accounts.

Analytics has integration with Adsense that is 'readonly'
Would it be sufficient to give an Analytics account for your partner access to the domain?

maybe you could use adsense's inbuilt reports thing, and set it up so it emails him the stats every day.

Actually for what you want to do, you probably want to take a look at Google Ad Manager. As far as I know, AdSense has no different levels of access.

[google.com...]

Netmeg is right. AdManager will let your designer generate reports and even place orders if you so choose.

Thanks for the suggestions - quite a few possibilities which I will look up.