Here's a good source of informal research that I almost never see mentioned. If you a developer for an existing product that is already in use at one or more companies, find out who the companies are (your sales department can provide) and contact their IT department. Helpdesk and desktop support people are on the front lines with users on a daily basis and know first hand what users struggle with. Talk to them. Pick their brains. Support professionals are often treated as the flunkies of an organization, and most I know would quite generously share their knowledge with anyone who treated them with an ounce of respect. Keep in mind that IT people often serve as usability experts in disquise, as they frequently must find ways to simplify and work with badly designed software and hardware that they have no power to change. So, some may even be able to offer some good suggestions as to how to correct the issues they've seen. Many IT organizations also keep detailed case records within their call tracking systems, and if you're real nice to them (ie.. feed them cookies), they might even get you some statistics on the number of calls related to a product or issue.

Though this method is not as effective as carefully designed user research, it is a good alternative when a company will not allocate any resources towards such a project. You may be able to gather a lot of information in a short amount of time, at no cost, and make a new IT friend in the process.