I really like being able to use the keyboard for everything, I was thinking a useful way to speed up the typing of umalts would be if we could use the up arrow to convert the previuos character to have an umalt. So if I type "u" then hit the up arrow, it will convert that character to having an umalt.
On my MacBook Pro, it's Option+u to activate the umlaut and then whatever vowel I want under it. More codes like that are listed at http://tlt.its.psu.edu/suggestions/international/accents/codemac.html For Windows, I couldn't anything analogous after searching the 'net for a few minutes and I left my work computer (running Windows 7) at work so I can't play around and help figure out a nice shortcut.
I use a Mac as well so umlauts are easy. As for Windows, you used to be able to hold down the ALT key and enter a number using the numeric keypad to get a "ü", for example. Then you release the ALT key and the character will show up. Here's a site that should help: http://bit.ly/aytLiC (turns out that's the same server as the URL mlabrum mentioned above). From that web page, the ü character is generated by holding down ALT, then entering 0252, then releasing ALT.