It's really quite annoying that some web sites circumvent Safari's integrated (very secure) access to encrypted keychains. What I'm specifically referring to is the tactic of preventing your browser from remembering web site login information and entering it the next time for you automatically, provided the keychain itself is unlocked.
However, certain sites, such as Yahoo, shouldn't have this ridiculous block. It's frustrating and annoying.
There is a way around it in most cases, though I have one particular site I visit that is extremely annoying (http://nextcat.com - is a social networking site) in its method of preventing one from storing login information. All the work-arounds I've looked at so far are ineffective for this site, so they must be using another method of blocking.
Autocomplete Always On! is a little Applescript application that will do some hacking for you of the Webcore engine, allowing you to store login information for MOST sites (except sites like Nextcat). You can handle this hack yourself using the instructions here, but I chose to use the AAO app above. Make sure you back up your Webcore too with the Applescript, just in case (you won't really need to, but I'm a worry-wart).
There are some other methods for doing this, using a Python script run through Pith Helmet's Machete function. One must remember to save the script as a plain text file with the ".py" extension and then make it executable, which can be done simply through the Terminal using instructions here.
But the method described earlier using the AAO Applescript seemed like a quick, global fix for my personal situation.