These all come from actual museum websites I’ve been browsing this morning:

1. Music that plays automatically.  Double-plus negative points for being horribly twangy.
2. Navigational buttons that are in flash only.  Plus 1 for having text links of the same at the bottom, minus 1 for not repeating them on subsequent pages, minus 1 for the flash not doing anything cool (why bother?).
3. Having a nice design, but no content.  Seriously, not even a location.
4. Using a difficult to read font.  (Incidentally, has anyone ever noticed that a lot of history museum websites use the same font?) 
5. Using a speckled background.  Am I the only one that finds text difficult to read on such a background?
6. Asking for credit card information on a non-secure page.
7. Using pdfs where actual webpages would be best.
8. Having a badly designed/malfunctioning website, and including promo information for the company/individual who did it.
9. Using frames without a solid reason (I can’t think of what that reason could be, but I’m willing to keep an open mind).
10. Inconsistent navigation.  See #2, but it isn’t that hard to repeat your navigational element on all pages of the site.  And I do mean all.
11. Not creating a 301 redirect for a frequently-accessed page whose link has changed (yet Google still includes the old page on the site links).  If you’d go to the trouble of updating your sitemap, Google could significantly reduce the number of people trying to access the old page.
12. Linking to a page whose title is an acronym (for heaven knows what), and then simply saying “Page under construction” once we get there.  Couldn’t you at least tell me what the acronym stands for?
13. Having a newsletters page, and the most recent one is from 2006.  Are you still in existence?  What happened?  Do you not have a newsletter anymore?
14. Having a site/hit counter.  This, even more than the frames, is so 1997.  If you want to know how many visits you’re getting (and you should), there are lots of ways to do that, and none of them involve a hit counter on your front page.

Now, all of these things are easy to fix.  If whoever did the webpage in the first place was capable enough to cause one of the above problems, they can also fix it!  (And doing so is my sincere recommendation.)

If in doubt, here are two resources to help:

Web Site Usability Checklist

MIT Usability Guidelines

Photo credit, mafic