Quickly entering attendance with barcodes
Maurice - we did something similar for a large event this year with multiple series of workshops running simultaneously. 

Every participant was pre-registered in Civi. Each workshop was added as a separate Event in Civi. We printed barcodes of the participants' Internal Contact ID onto cheap Avery mailing labels - something like 3 inches by 2 inches - using the Event Badge template in Civi, and just pasted the labels on the back of the registration badge holder. 

We then created a shared spreadsheet in Google Drive, with a worksheet for each workshop, and set up a volunteer at the entrance of each workshop with a wifi-connected laptop and a USB barcode scanner. 

All the volunteer had to do was scan each bar code into the worksheet. It worked pretty well. One hitch was the size of the bar code produced from Civi is a little small, and we used cheap (we got them for about $10 each) old CueCat USB scanners I found through eBay. We then just imported the Participant IDs and updated the Event status for each workshop Participant as Attended.

Just in case, we had plain old paper sign in sheets for each workshop available and used those in some instances.

The biggest challenge of this technique is having enough volunteers, with available laptops, set up in advance with the USB scanner (and the correct driver software!) and decent wifi. Wifi isn't required but it was handy to have the scanned-in Internal Contact IDs for each Participant appear live in Google Drive while they were scanned in for the workshop.