Just now I've needed to copy some files (directory with about 4 files, 5.4GB on 8GB flash drive). The flash media AFAIR supports USB 2.0 (by my PC has also some USB 3.0), connected to USB 1.1 port. At the start of copying thunar showed only about 3 minutes. Minutes (many minutes) gone. Now more than 1 hour passed. Thunar shows 19 minutes feft before finishing of copy. Also, thunar doesn't shows percentage (complete/left). The algorythm of time computing needs in improvement. It should depends on connection type (IDE/SATA/SCSI connected hard drive, USB-1.1/2.0/3.0 connected media). Also it will be good to improve interface: Making it show not only line, but numeric percentage of complete/left time/data. Check data size, where current algorythm shos sufficient results and if copied more data show only digits of persentage, not time.
Excuse me. Something strange happens: First 4 files (5 within direcory) were copied in more than an hour. But after that I've copied ~1.4GB file to the root of the same flash. It was copied in about one minute...
It uses the transfer speed in 1.5 which is somewhat more accurate, but the problem is within linux. First portion is going very quick (caches) en syncing starts and the speed drops.