Provide the user with files size and time estimates located immediately next to the link of the large image or file. If a large document is available on PDF, also provide a straight HTML version. PDFs are not always wanted and browsers do not always have the appropriate plug-in. The last thing users want to do is to download a plug-in, or even worse, another browser, just so they can view your particular web page. In summary, slow download times aggravate customers and greatly increase the likelihood that their visit ends in failure from your company's perspective.
People hate horizontal scrolling.
This Undeniable Truth is simple enough, and true for any computer interface. To explain, this web page is too long for you to see on one screen, so you have to scroll down to read it. That scrolling is vertical. People have a very common, strongly negative reaction to horizontal scrolling on web pages. Most web pages designs do not intentionally require horizontally scrolling, though some surprisingly do.