Select And Tag Multiple Notes

If I understand correctly, this is actually already possible.
You actually can select more than one note via Ctrl+Clicking on them. Or if you want to tag all untagged notes, select "Untagged", then "Edit/Select All", then "Edit/Tag".
Or, from the keyboard [assuming version 1.6 Beta2+]: Ctrl+U, Ctrl+A, F4.

The lockup only occurred once, so far, and then when I tried again, not all the notes were retagged.  However, I restarted the program, and so far have not been having any issues.

This seems to work sporadically -- at least on my system.  I just tried it three or four times, I found it worked once, then tried it again with mixed results.  On one attempt the program seemed to lock up.  I only tried to tag about six notes.  I'll continue to test this....  

Could you please describe what exactly you're doing to lock the program up? Are you using 1.5.7 or 1.6beta3?