LibreOffice is a product used by people of all ages. See what I mean, do you know a lot of secretaries using Ubuntu? (I like Ubuntu, it's not the question). Do you know a lot of students doing the accounts or prospective on Calc? I know about few of them, but not the majority. Our product cover a large range of usage, and touch all sort of people. This is quite unique for an open source product that works on all platforms. And so is the difficulty to design an interface that will please everybody. You know also that LibreOffice is based on OpenOffice.org which in turn was based on StarOffice. Long life old things.

The design project has two faces, one is for the product, the other one is for all the designs needed by the community. Lets begin with the product.

There is a lot of work going on there. Have a look to the wiki, it's very well structured and organized : http://wiki.documentfoundation.org/Design. As usual the main door is the mailing list. You do not need to have special design skills to participate. As the one who use the suite every day, you're opinion is of great interest. If you have design skills, make your proposal on the list and upload your work to the wiki. But for better work, the project is organized, so please try to follow what's going on, it's better to avoid to go in all directions at the same time :). If you want to follow more closely or point to your new proposal, you can attend the irc meetings organized each week on the freednode server at #libreoffice-design. The log of the discussions is uploaded also on the wiki see the notes form the meeting at the beginning of November, for example.
The team is not working alone, it has frequent exchanges and interactions with developers and users. It's not enough to make good mockups, they need to be possible to code too! They organize surveys for example to analyze users behavior or test new design. So even if you really don't feel comfortable with design, you can still participate here by helping setting the surveys or, translate it in your language so that we gather more participants from every where in the world. Spreading their work will help the project to get more feedback and visibility, a good thing for a product of that importance.

If you have not enough time to participate through the mailing list or the wiki, you can get in touch with the project through its Google+ page. You can even post your contribution from here! And all is not about dialog boxes, or icons, it's also about templates, colors, or splash screen.

I told you about the other part of the design project: answering the design needs of the community. For example, for the donation campaign, we needed a banner. Or for the next Fosdem, we need tee-shirts, or what about a banner for the new year greetings, or what about postcards, posters, calendars, or what about series of design for goodies ? I'm sure the marketing project has a lot of ideas on this topic.
So a lot of room for your creativity, just express your self and share it with all of us. You'll get feedback, encouragements, welcome, and a big hug from the community for your realization :)