Many indies know they should think about trademarking; it's on the (long) list of things to do, but funds are tight and they feel they have to allocate the money in other ways first. They want to build their brand first, and once their brand gains popularity they feel the time is right to think about protecting it. The problem with putting your time, energy and money into marketing and packaging and website development first is that you may be investing in a mark that may be not worth strong protection, or at worst, infringing on someone else's rights.
Ideally, the best time to work on obtaining a federally registered trademark is while developing the concept for your brand. A forward-thinking client will present a few options to me for a developing brand, and I will perform searches and let them know of any red flags before they make the decision to move forward with a mark.
Even if you have already been using your mark for some time, there is no time like the present to move forward with protecting the brand you have been building. The cost of obtaining a registered mark is well worth the protection it affords, in more ways than one.