Is it worth a back-end developer's time to get into web-design and HTML/CSS
phoreo: I straddle the line between these worlds.  My day job is frontend development with some Ruby here and there, while I've been designing and building out a Rails app on the side.I think my response would be similar to your 'developer-side' response - if at any point in working on a project I find myself confronted with something I do not understand, I have this compulsive urge to figure it out.  In the process, I've saved myself thousands of dollars by investing a few days to learn what I need to at the time to get around the problem.It sounds like you're a great Ruby developer with a leg up on all of the new "ZOMG RAILS!" converts.  Don't be too concerned about the "jack of all trades, master of none" category.  If you're working on building a company from scratch, product guys/gals are key - people who may not be experts in everything, but can get the job done for rev1 no matter what.  If you can play that role yourself, you'll have far fewer people to depend on.If you decide to work on the frontend yourself, start with raw HTML and forget that CSS exists entirely.  This might help you to think of HTML/CSS as a backend developer.HTML is just XML with a fixed set of elements that are named according to their purpose and have specific functions in a document - and you'll probably only need a small subset of them.  So, look at your comp and think of the elements in it; paragraphs, lists, images, buttons, links, etc.  Then, start writing what seems like an XML document describing it.  Again, don't even think about styling it at this point.  Just build the best web page that 1994 ever saw:  <html>
    <head>
      <title>My Application</title>
    </head>
    <body>
      <div id="header">
        <div id="branding">(Name, logo, etc. here)</div>
        <div id="nav">(Navigation)</div>
      </div>
      <div id="content" class="column">(Main app content)</div>
      <div id="sidebar" class="column">(Sidebar content, if you have one)</div>
      <div id="footer"></div>
    </body>
  </html>

Once you've got your document written, you can start to tackle CSS.  Since you've got a valid, well-formed document composed of semantically-meaningful elements, you'll find it much easier to style than people who focus upon the look of the document as they write it rather than its well-formed-ness.  If you choose to hand it off to a dedicated frontend developer at this point, they'll be grateful that you've provided them with a solid canvas to build on.Good luck building your application; whichever route you choose, let us know when it launches!And if you'd like any recommendations for either a designer or just someone who can slice and dice a comp, let me know; I've got a few solid friends who charge reasonable rates and have some availability coming up.