I studied them in my high school Latin class. There were just 12 of us in the class. Due to a bad strain of flu that winter, our final test on Catullus was postponed 4 times as various people were home sick. By the time everyone was back in class, we had studied them so thoroughly we knew many of the poems off by heart...
So 34 years later, I can still recite "Odi et amo, fortasse requiris, ..." and "Sirmio, gem of islands and peninsulas, ..." [peninsula = paenae insula = almost an island :)].
Another interesting side to Catullus comes from the music of Carl Orff. He is of course the composer of Carmina Burana, a collection of medieval drinking songs, with the most famous being O Fortuna! [1]. He also set Catullus's poems to music, in his Carmina Catulli [2]. [3] is a version with the musical score in the background.
Here are two other Catullus resources for anyone wanting to learn more:
* Bilingual edition by Peter Green - Latin and English on opposite pages: https://www.amazon.com/Poems-Catullus-Bilingual-Gaius-Valeri...
* Wikipedia has a very good list of all Catullus's poems: https://en.wikipedia.org/wiki/List_of_poems_by_Catullus
[1] https://youtu.be/GRjyxr1ysKw?t=77 (O Fortuna starts at 1:17)