I would like to add 20-30 users to a SharePoint site (Members group). Unfortunately, the Add Users interface is excruciatingly slow (nearly a minute to browse for a single user). Can it be done in bulk?
If you know the users email addresses, you can add them in bulk, delimited by a semicolon.
email@example.com;firstname.lastname@example.org ...etc or by domain account domain\user1;domain\user2;domain\user3
You can use active directory groups if one exists. I've even copied users off of an email before and dumped them in, you might not get 100% matches always, but it can be faster than looking them all up.
Wouldn't it be smarter to find out, why your "Add user interface" is so slow? If you say that it takes a minute to add a single user, I guess that the people picker needs that long to resolve the user in AD, right?
So, if that is the case, try to limit the scope of the people picker using stsadm. In this article you will find the commands you need. http://www.synergyonline.com/blog/blog-moss/Lists/Posts/Post.aspx?ID=5
Hope that helps.
Take a look at SPDash, it does exactly what you're looking for. I've used it to manage multiple site collections and it works great.