Second: I suspect there's still room for improvement. White text on a solid brown rounded rectangle with slight drop-shadow gives a fair button/click-here hint, but is still not as strong as I've seen elsewhere.
Some companies who thrive by download rates (Adobe Flash, Apple ITunes, Skype) use brighter colored buttons, with a faint gradient, and possibly a down-arrow icon, mouseover highlighting, or a contrasting border.
You may also want to compare against a large text 'download [filename] now' link with strong hyperlink hints (blue, underlined).
i'm looking at building a "purchase!" button, that's obviously quite important in the whole scheme of my site, so i'd really appreciate anyone pointing me in the right direction...
Jakob's "Law of Web User Experience", which is "users spend most of their time on other websites", is also a good guide. Study and mimic the best practices of other more popular sites that use the same sort of 'download'/'purchase'/'add to cart' button. They've done the testing and trained the users; novelty usually confuses.
2) Lots of shareware trackers check an industry-standard file on the app's web site to learn about updates, drawing more attention to apps that are "new" or "updated."
3) With a software product, as with web apps, the goal of your site is to get the person to use your product, if not pay for it outright. Therefore, there should be an actionable prompt to download the software on every page (though not always in the form of a big red button, of course.) As most visitors leave the homepage of most web sites they've never been to before right away, there should be something for them to do.
I bet many people click the download button so that it can download before they figure out whether they even want it. I do that all the time. If I read more and I decide I want to install the software, it is already on my desktop waiting for me. If I read more and decide it won't work, I just delete it.
A fair number of people are petrified by the idea of spyware, and bail out of an installation when encountering normal warnings.
This is a whole lot more annoying when websites do it with stuff that you're not interested in, like ads.
I prefer sites that look natural than loud. A big download button doesn't mean loud necessarily.
At least that's what I think.