Well, you can. But it's only viewable to you. It is stored on your personal BAM! account . So if somebody else (with a BAM! account of course) sets a target for the same user/host/team/whatever it is stored in his account separately from your target.
Or I must've made an incredible stupid error, let me check..... Nope, I didn't.
To demonstrate, I just set a target for your combined user account to 500000. Check it, you can see your own target is still shown on the page.
And happy to say already 1615 targets have been stored.
Also, your suggestion to only show the target calculator for your own stats: that would mean that people without a BAM! account can't watch a target (because without BAM! account, how to know it is your stats page?). Although this might convince some people to take a BAM! account (it is worth it!!) I decided to enable it for everybody. But, when you do not have a BAM! account (or are not logged in), the target is not stored.
Ow, and finally: if you login to BOINCstats on another system, your targets are also shown there, so it's not depending on a single system.
Please do not PM, IM or email me for support (they will go unread/ignored). Use the forum for support.