Scaling limits

I'm wondering where CiviCRM 2.0's scaling limits are. Understand it depends somewhat on underlying hardware/database/etc. But I'm interested in where people have seen the software fall over in terms of:

1.Number of contacts
2.Number of groups
3.Size of a group
4.Size of a search result set
5.Number of mail recipients in a CiviMail mailing
6.Number of mailings
7.Number of tags
8.Number of custom fields
9.Number of search critieria
10.Number of relationships
11.Number of profiles
12.Number of ACL's/roles

See the responses and discussion at http://forum.civicrm.org/index.php?topic=4919