Nice a topic I know a lot about on HN
Mechanical keyboards are more enjoyable to type on for one so that's something to consider on it's own. In terms of your pinky getting sore after long usage it might be less likely to occur with a mechanical keyboard because most mechanical keyboard switches don't require you to press as hard to register a keystroke compared to a non-mechanical/rubber-dome keyboard like the one you have.
Most mechanical keyboards today use Cherry MX switches, there are a variety of different Cherry MX switches to choose from. Some are louder than others and have a different tactile feedback. A good reference to get an idea of what I mean can be found at this link here: http://www.mechanicalkeyboards.com/mechanical_switches.php
It's a bit difficult to know which Cherry MX switch is right for you right away, you can narrow it down to some degree beforehand but it's difficult to have much certainty of which you'll like best until you try them. You can visit your local computer store (Frys, or if you're in Canada than Canada Computers) and try some out there. Otherwise you can order a switch tester: http://www.cmstore.eu/cm-storm/keyboards/mechanical-key-swit... and decide from there, Coolermaster will also give you a discount on your mechanical keyboard if you buy one of their mechanical keyboards from them after purchasing one.
One of the most popular, entry-level, mechanical keyboards is the Coolermaster Quick Fire Rapid and the Quick Fire XT. It's a safe purchase and good value.
There are a bunch of other factors to consider with mechanical keyboards as well than would take forever to get into here. Some of those factors would be keyboard layout, the standard layout is what you'll see on the Quick Fire Rapid/XT (i.e the backspace/shift/enter keys are the standard sizing/spacing).
Another consideration is what type of keycaps you want on your keyboard. You can buy aftermarket keycpas for premium that are usually better than the ones that come with you keyboard, and with mechanical keyboards you can easily replace your keycaps. This is where keyboard layout, as mentioned earlier, is important because if you want to replace the keycaps at some point it will be difficult to find a full set of them for a keyboard with a non-standard keyboard layout.
In terms of ergonomic mechanical keyboards some exist but they aren't that prevalent. I would recommend getting a keyboard with a standard layout and progressing from there if necessary.
If you want to learn more check out the Wiki on reddit for the mechanicalkeyboard sub: http://www.reddit.com/r/MechanicalKeyboards/wiki/index
and if you have any questions you can ask them there are well, there is a thread stickied at the top for people to ask questions.
As another user mentionned deskthority and geekhack are good resources also, although they have more of an established community and although helpful are less eager to walk newcomers through the buyer process. They would prefer to answer more specific questions with regards to mechanical keyboards, as opposed to the 'what keyboard should I buy if I should even get one in the first place' type of questions.