The home page is confusing. The large thumbnails with captions are ambiguous: do they allow you to upload and organise or crop, fix, edit, or do they show you how to do it? I really miss having a global navigation bar that would allow you to instantly navigate to a users page, or a tags page. The search is prominent, but even some of the links to recent items or to geotagging are put in very small typeface, almost like an afterthought.
When you do get past the home page into a gallery, there is a very clear breadcrumb, making it easy to navigate up the hierarchy. There is very little distraction on the page, making the photos stand out, but it is a little flat. Icons next to each photo are a bit cryptic, and The navigation bar is still bad. There is home, tour, sign up, and explore. Everything useful is crammed into explore's drop down menu, instead of being prominent.
However, on the secondary bar, under someone's profile, there are very useful links to sets, tags, maps etc. making it puzzling why the main structure is so hard to navigate.
When you enter each photo, there is plenty of room for comments, and the sidebar allows you to navigate through a gallery and see extra information, like exif data. It is annoying that you can't view all photos at large size in line, you have to click through them, and that you have to click through another screen to resize a photo.
