In general, you acquire trademark rights by use in commerce and not merely filing with the US Patent and Trademark Office. So those who are first to use, even if they have not filed to protect the same yet, have priority of rights in their marks (i.e. You!). If $350 is a lot of money for you right now, then I would hold off, otherwise go for it. It's my opinion that you don't need an IP lawyer for this. It's easy enough for anyone to tell you that you do need an IP lawyer because it's a mildly safer route depending on how diligent you are and they're not the one's shelling out thousands of dollars on it. It's a simple enough process to do on your own. If you want to feel better about doing it yourself, buy one of the Nolo books on this topic and spend an hour reading up on it. It's also my opinion that you want to know how this stuff works anyway if you're thinking about becoming an entrepreneur.
Another option is to have one of these legal websites (LegalZoom, RocketLawyer, etc.) file it for you. They'll charge you about $150 over the cost of the application, for a total of about $500, instead of $350 doing it yourself. The benefit of doing it this way isn't that you have legal experts processing your application, because they're not lawyers, not even close. The benefit is that they are very familiar with the common errors and reasons that many trademark applications get denied by the USPTO. The other benefit is they do a fairly comprehensive trademark search for you, even when you pay for the most basic package.
Don't forget you'll need to file an additional application, once your product goes live to inform the USPTO that your product is in use. This will cost you more money, though not as much as the Trademark application.
In the U.S. you may claim a trademark by right of first use and using the "TM" identifier. Registration with the PTO is not required to claim a trademark, but it does give you a number of important additional legal rights and privileges including the right to use the ® symbol and ability to litigate a trademark dispute in federal court.
See the highly readable overview of trademark basics at the PTO for details.
I am just completing the registration of two trademarks that I've been using for about a decade. I've done the registration without the assistance of an attorney.
Only you can determine whether you should or should not register a trademark. :-) There are several factors to consider in this, some of which are the level of investment in the brand, the SEO value, and how 'big' a deal this startup is for you personally -- is it just a side project, or something you think could potentially change your life completely...
With regards to branding, I think behavior is radically different between small companies and large ones. If a small startup sees you have the .com domain in active use, then the startup competitor will skip this name and find another name for their own products. If Cisco, Microsoft, etc. have their sights set on a brand for a new product and realize that the domain is taken, then they just see that as a small obstacle. Most likely they'll try to buy the brand & domain from you, but potentially they'll just steamroll you instead. In this case, the trademark registration is quite cheap for you, yet offers strong protection against their steamroller.
Registering a trademark is one of the few legal activities that I think can reasonably be done by a non-lawyer. Get a book, or find a guide online, and go for it. It's mostly about research, and then filling out the online forms. Have a look at the past discussions about trademarks here, somewhere in there is the link to the online US and EU trademark applications.
I believe the answer given by Jesper is spot on, but I would like to expand on his last point. Whether you decide to get a trademark or not, you really can handle it without relying on a lawyer. It sounds to me like you're going the bootstrapping route. Save your law "budget" for a rainy day. To have an enforceable trademark in the US, you simply need to add the 'TM' symbol. To have an ironclad one, apply for yourself at very little cost.
Surprisingly, the USPTO website is actually an excellent resource. It contains everything you need to know--straight from the horse's mouth.
It depends on your market and competition - a trademark will give you some protection and prevent people from bidding on your trademark in google adwords (like your competitors)
I would get an IP lawyer to do it and in your local area - you can at a later date file in The Madrid Protocol (covers a group of countries).
Unless you are prepared to actually defend the trademark and go after people then I would say not yet.
I agree with other that at the very least you can use the TM for unregistered trademarks.