I've founded a few startups over the years, and as a glutton for punishment I'm doing it again now. I've not trademarked anything for any of them though, and here's why.
As you doubtless already know, startups are really hard. If you're just going into beta you will have more than enough work on your hands just managing your test, and when you do get free time you should be spending that on new tech and features for your site.
All this assumes that you're a small bootstrapping team of hackers of course. If you have enough time and money, it might be an avenue worth considering, but even then over 90% of startups fail, so you'll be trademarking something that might not even exist in 12 months.
At the end of the day your logo and name really don't matter as much as your product, which really doesn't matter as much as your passion. Focus on quality and traction and you'll build a successful business.
I'd be happy to schedule a call and talk more through it - just let me know.
