rahulsundaram wrote a bit about the current development of yum, and what the new release for Fedora Core 6 will bring to the average user.
The most important thing for all the speed stressed people will be the news that the new metadata parser is written an C and works much, much faster. If you don’t now what the metadata parser does: well, everytime you start yum in the shell and look at some “#####” getting more and more, that’s the parser. The speed improvement is given as 45.5 seconds with the old yum compared to 7.17 seconds with the new yum.Pretty impressive, I think. Speaking about speed, there were also some changes in the mirror system which look like that we get localized mirror lists again (at least more or less).
There will also be a new plugin which checks dependencies before yum starts to work – that adds the ability to continue working with yum even if one or two dependencies cannot be fulfilled.
Speaking about plugins, it looks like we will soon be able to access delta-rpms – in this case, however, we need someone providing these delta rpms, and I haven’t heard of anyone setting up a server system yet. But the Suse guys have something like that, so maybe you can soon use Suse’s delta-rpms with yum.
And last but not least I want to mention another nice improvement: when you now (= with version 2.9 instead of the FC5 version 2.6) press Ctrl + C while yum runs it does not jump to another mirror – it quits. Just nice – and what you expect.
/home/liquidat 
delta-rpm seems unfortunately badly designed. Mandriva attempted to implement it, but has failed
See http://qa.mandriva.com/show_bug.cgi?id=24535
Hm, interesting. Suse did not have such problems, also the argument that it breaks rollbacks is a bit strange because rollbacks are also accounted as poor designed and not reliable functioning (afaik).
Let’s see what comes out of it 🙂