So, what you often hear is that your running shoes are good for 300-500 miles. But, how many actually log their miles? I'd venture to guess not many(present company included).
One trick I learned eons ago to check how much life you've got left in your running shoes is to take one off and try to fold the front of your shoe in half (almost like a tortilla). What you're trying to do here is test the midsole of the shoe (typically the white foam like stuff that's in the MIDDLE of the shoe).
If the shoe folds in half with minimal effort on your part, chances are your midsole is just about done. If on the other hand, the midsole does NOT fold easily, you've likely got some life left in your running shoes.
Ultimately, what you should be most concerned about is the midsole, not the outsole (the typically black part of the shoe with the tread). It's the midsole that's providing you guidance, support, cushioning, etc. Once the midsole's shot, you're opening the door to potential injuries/aggravations.
In the event your shoes are done, the crack crew at Fleet Feet Sports San Francisco can get you back on your feet in short order:
I used to do my running in some heavily padded shoes, such as basketball or cross training shoes. Then I got the Nike Free shoe. Wow. They are pretty much the only shoe I train in now (which is probably not advisable, you can fold them into tacos and hamburgers!). They let me make my own movements with out restriction but keeping my feet protected. They help develop the intrinsic muscles in your feet, which can help you with other sports. (I could defintely feel it too). It takes some getting used to, you have to gradually get into wearing them. And you can feel the difference. It's amazing, but they should be worn as tools for better performance and defenitly not every day around around-the-house wear. See what Poiatry Management has to say about these and other foot wear that claim to have the latest techonolgy. (including shoes with computers :-D )
You're not alone! Orthotics 'can' help, but it doesn't mean that EVERYONE needs them and they are necessarily a panacea.
It's commonly the case that orthotics (store bought or custom) need about a week or so to break in, so this isn't unusual.
SportsBasement is great, but if you go to a running specialty store they typically watch you run closely and can better identify the shoes that are best for you based on the kind of runner you are.