In a discussion with co-workers today, I lamented that I can't ever remember what an icon means, and have to hover over them to see the tooltips, and thus to find the button I need.
On their side, they were saying that when the text needs to be translated, it might not fit (German vs English for example), and that every place where there is text, including tooltips, it needs a translation. So plain icons are easier.
What is the best tradeoff in useability for the extra work of text vs the subset of users who are icon-challanged?
I personally prefer text and hate icon-only UI's. I know that other people think the other way, equally strongly, either because of internationalization or because their brain works more rapidly with images than with text. If you choose one or the other exclusively for your UI, then part of your user base will be unhappy with your choice. (Sometimes this is the right choice, depending on how extensively the UI will be used.)
Internationalization is really not that difficult, except for finding a firm to do good translations of your text. The programmer portion of internationalization is pretty straightforward. However, I've known a number of programmers who prefer the all-icon method as it's less work. I've personally had to replace one all-icon-no-text UI that the users didn't like. The users said they could not remember what the icons meant.
I think more typically, many advanced users will prefer icons and many beginning users will prefer text. However, a number of advanced users prefer text. IMHO, any good UI will provide tooltips, so you need to translate your interface no matter what you do.
The most friendly solution is to offer both text and icons, possibly with a settings choice to disable one or the other.