Yes, yes, you should absolutely include this information! Here is why:
1. In the screening process for interviews and then in the final score for applicants, many schools use a rubric system that includes "research." Even if you haven't conducted research yourself, you have been sufficiently exposed to the process and wouldn't want to miss out on getting "credit" where it's due. Your familiarity with laboratory technique, the frustrations of attempting to get manuscripts published, etc. are fodder for interview conversations.
2. Admissions committees are interested to know how you spend your time (extracurriculars, hobbies, work, etc.). If you were in lab, then you weren't doing something else that might have otherwise bolstered your application. You want your time (and hard work!) to be accounted for.
3. Admissions committees value commitment. You have demonstrated commitment to your lab given the amount of time you've been there. If at all possible, in your description try to demonstrate advancement, ie taking on more responsibility, managing other people, etc.