For students answering online exercises, we do not use assessment, but our own system
https://nm.wu-wien.ac.at/research/publications/b318.pdf . We have up to about 1600 concurrent users, most of the solving exercises.
For course evaluation, we use assessment module, but only in a few parts. Currently, we are running evaluations for 1200 courses reaching most of our students (20000). We do this currently not online, but based on a paper & scanner based solution. We have quite a complex system tailored to the needs of our university. We have plans to offer the teachers in addition to the paper based system online assessments but this will need some work to run smoothly in this scale.
In autumn we were running a few smaller assessments (a few questionnaires for a few hundred students each) with mixed experiences.
Our 'learn' system predated .LRN, but was merged when .LRN came out in parts. Last time, i checked, our system differs from OpenACS/.LRN in about 15.000 changes.
We are not only running the learn system, but have about 20 OpenACS/.LRN sites within the university for various purposes, and similar numbers for customer sites, supported through our university spin off Knowledge Markets https://www.km.co.at. Knowledge Markets runs a site for customer assessments https://www.evaluate.at/ using the assessment module. It runs there with the mentioned changes, but i cant say, how many simultaneous assessments are usually filled out there.
