Actually something that not all designer check is how their website looks on different systems and also different browsers. It often means you have to have multiple computers and also multiple browsers installed to be possible to test them all. However the most run systems nowaday are just Windows and Mac Os ( I know Linux Unbuntu is also one but small categorie). But there are way too much kinds of browser you have simple Internet Explorer, Safari, FireFox, Opera, Flock, K Melon, Navigator, SeaMonkey, Shiretoko, Avant and ofcourse Chrome. It takes way to much time to load it up and check them all, but there is an easier option.
Go to Browsershot.org which makes screenshots of your website in all the browsers and you can view them online however they will be kept there for only 30 minutes. You just have to select which systems and browser you want to see and type in your url press ok or send. Also they have a download option where you can download the shot in a zip file. How ever they are not neatly aligned like above but are loose shots of each browser and system. It is a totally free service and lets you see all the fault in other browsers. However most Unbuntu browsers plus unknown have most errors and does not need most attentions. But the most problem is the same standard font inside a PC is different then on a Mac, and they have different sizes and shapes gives problems. But also people complaining my site to have too small fonts and now was first time to see why but was not cause by Mac or PC but Unbuntu and that person must have been using a NetBook.
Also some browsers does not work with CMS sites or DHTML codes. There are few that does not show anythings at all in the browsers. But most systems looks very fine. But actually wondering how my website would look like on mobile phone systems though. Maybe I should tip them about that so I know my website looks good on a iPhone and on a HTC for mobile internetting.