The biggest sign that a job is good or bad for your learning is whether or not you are learning new skills on the job. You should be picking up at least two significant skills that will change your resume per year, in my opinion. Yes, there is always boring work; but it shouldn't be your entire job for long stretches of time (but short stretches - a couple months or so - can easily happen during 'crunch' periods).
If you aren't learning on the job, talk with your manager. Maybe you are doing new things, but not recognizing them as new skills; or maybe your manager needs to re-balance workloads so you aren't always getting stuck with the familiar, easy, boring work. It's also possible that you are learning things, but not in the direction you are willing for your career to ultimately go. Talk, and try to find common ground. This kind of problem can often be a win-win, so work closely with your manager to find a solution.
If your job is still all non-challenging work a few months later and you have been working with your manager to get the situation to change with no results and no reasons to expect real change soon, you are not working at your level and should consider hunting for a more challenging job. Moving on should be good for your business as well, since - if they are paying you what you are worth - they should be able to replace you with someone cheaper.
Of course, this does not go against the advice to do personal projects, read a lot, and so forth outside of work. This can greatly accelerate your career. However, your career should not have to become your life for you to progress at all. You should have some career velocity even if you do just 40 hours per week and then head home to your family - at low levels, you should be getting a small promotion every 2 to 3 years with just 40 hours per week, and at high levels, you should be at least holding even (e.g., not going out-of-date). This does depend on your team - some workplaces are so good that people just don't move on, and it can take years for a spot to open up so you can be promoted. I'm also assuming that you are actually working as hard as you can during your 40 hours.
If you still aren't sure how your company is doing because you simply don't have the perspective, start scheduling "informational interviews" with developers at other companies. These are interviews where you just learn about that company and how they do things, and they have nothing to do with seeking a new job. They can be a great way to get some perspective.
Bottom line: Your company (and your team) should care about your career, just as you should care about the company's growth and success. If you don't think your employer is concerned enough about your career, "Vote with your feet" - that is, walk out and move to a company that will care.