1) The most immediate thing I notice are the three superfluous search bars on the top left. Yes, Lojban is a wiki, but Lojban is also an informative website representative of the LLG and the language as a whole. The wiki features should be off in a separate section of the site making themselves less apparent, because most of your views are from people who have no clue what Lojban is and no less than one minute's reading time to find out.
2) Main Menu: There's no reason why you need every drop down option exposed like that, but, more importantly, every menu item should be central and preferably on the top. Take this for example:
Every menu is a simple, clean button that makes for easy access. You can still keep everything, but you need to prioritize the information. Stuff like links to a Lojban song should be *very* deep into the page, whereas at the moment you have equal chance of stumbling across a Legend of Zelda translation of Lojban as you do the Lojban mailing list. Which brings me to another point:
3) Graphics. Not very complex ones, but still--the Lojban page is *very* uniform in its colors. Even reddit.com, in its text-based glory, uses colors to make its links stand out from one another, and digg.com does the same. You can use colors and icons to separate key categories visually. A great example is the main page of Lojban's very own Matt Arnold.
4) The news doesn't look like it's actually news. That is, there's no visual indication that brings the user to it saying "this is news", it's just text like any other text.
5) Speaking of text, Lojban's website text is very large. Verdana size 12 or Times New Roman size 12 are eclipsed by the behemoth that is the current font.
6) "What is Lojban?" on the main page, followed by information about the LLG. Nearly every website has a very distinct "About" button, but if you must explain the language upfront, take notes from ubuntu and try not to go too deep into explaining what Lojban is on the page people immediately see. Save that for an in-depth page.
7) Livejournal and forum/mailing list meshed on the main page. Currently, the displaying the Livejournal posts makes the page enormous, and displaying the mailing list as a forum tricks the first-time viewer into thinking there is virtually no forum activity despite that mailing lists behave very differently. I'd say get vBulletin, get a "shoutbox" plugin which serves as a chat (but don't display this on the main page), and a "top 10" plugin for the main page (but display the font in tinier text than the main font--if you use size 12, make it size 10 or less) and then be done with it.
8) I'm not sure who updates the site, but it really looks bad to have News that hasn't been updated since a year ago. Even if it's really minor news, it's still activity. This gives the impression to someone that has never seen the language before that it's an obscure language spoken by a small group of geeks (note: I don't mean this offensively, I consider myself a geek as well) in their basement, and however accurate that impression may be, that doesn't mean that's the impression you have to give. Lojban is useful for not only science, but for law, and the impression you should try to achieve to balance both of these is that of a company like Mozilla or Ubuntu, which is still undeniably geeky yet able to work with stuffy professionals if need be.
9) Make donation and the fact that you're a non-profit more obvious, and allow donations to be done by a method other than PayPal. I would donate to Lojban if it were more like the donation system on Barack Obama's website, where I don't need to go through the hassle of PayPal to donate.
10) Finally, don't use tiki for every page. Simple web pages, though less 'open', would be more appropriate. As it is, the current tiki makes pages that should be simple and informative very convoluted.