I have ranted about Presto in my earlier blogpost. Yum's fedora maintainers implemented this really cool idea of maintaining difference between binary packages instead of the binary packages themselves. It would help a lot to push out updates. I was sceptical at first about the amount of savings it would result in (because obviously binary difference is something very complicated). I expected a 20-30% saving. Although people kept reporting numbers of upto 90%.
Today, I decided it was time to "yum update" my machine. (crashing pidgin, crashing rhythmbox, bad font rendering). So, I ran yum update. It showed me a total download size of 876MB (i.e. the total size without presto.. since, presto is new and under beta.. its integration with yum is only perfunctory). So, I dozed off. Today I check my internet usage and guess what, the total usage yesterday night was less than 100MB. Awesome! (Usually, presto shows the difference. It prints out a line saying "This is actual download size and this was download size with presto". But, as I dozed off, the line went off the terminal limit).
Anyway, it is infact 90% savings! that is so awesome! Now I can "yum update" even during the day :D. No need to wait for the night free time.