Which problems would you say are the most common to occur in today's sites?
Question's a bit too broad. There are sites devoted to this like http://www.useit.com/ (Jacob Nielsen) and books like Rocket Surgery Made Easy (Steve Krug).
And it depends on the site/web application purpose - is it a blog? a store? a web service?
And there are lots of specific answers on usability questions posted on this site addressing common issues. If you search under Usability you'll get tons of returns.
Subjective list of 10 things I see a lot that bother me the most:
- Can't find the search
- Can't find the log in
- No page title
- Not accessible
- Real Content in a pop-up (some will say just using a pop-up window)
- User error returns without meaningful or noticeable messages
- Crowding/no white space
- Not stating user or password rules
- Events that only work with a mouse
- No semantics, hard to see any organization and too hard to read
Some of the things that bother me the most:
The pop-up type adverts, particularly the ones that actually open a new tab when you press on the close button - unforgiveable.
No Contact Us option on a website (this is even worse than no About Us section). Links that pretend to be links but don't actually do anything.
Flashy-looking websites with loads of colour and poor text contrast - these are much harder to read text on.
Cursive, arty-looking text that can be difficult to understand.
On shopping websites where you are able to sort by price (asc ending or descending) reverting to the default every time you start a new search.
broad questions I don't mind; I can relay what's off the top of my head:
- checkout via view basket on ecommerce engines. just give me an option to go straight to checkout
- needlessly complex registration. give me email pswed with option to enter more complex info at my leisure
- tag clouds. may be useful, but can't find evidence base, use valuable screen space at expense of proven functional content
- blah blah text and meanlingless landing pages (this is the worst). landing pages should give concrete links elsewhere or provide useful content. all too often replication of left hand nav with utterly useless blah blah content
- pop up adverts. get off my page already.
- poor search results. Often fault of search algorithms and poor results display. Please highlight my search terms and keep the content to page title and abstract. thx
- large header graphics pushing everything below the fold. yeah, thanks for that.
Websites that are so focused on having a totally radical graphically modern and hip design and artistic flair that they forget to design the website for usability and comprehension.
Graphic designers are most prone to make their portfolio websites like this.