Examples of products with extensions:
Flow-www.getflowapp.com Highrise-www.highrisehq.com Harvest-www.getharvest.com
Anyway, in my experience, most people will either Google for your name or come in through a link. People typing your domain name into their address field are outliers. So I wouldn't sweat it overly much, in comparison to other aspects of your marketing.
For example: if I remembered Basecamp from a couple weeks ago... I'd type it into my URL bar. Had it been getBasecamp.com instead of basecamphq.com... it may not have appeared as easily. For my startup, I even go as far as emphasizing the first two letters so that people remember them (this is easy as it's "UP").
When picking a name, I would suggest that the first 2-3 letters are not the same as another popular website. For example: I would not name something factmaster.com because facebook would popup instead.
My advice is always to spend the time to find a good .com. Domains like MixPanel.com or HelloFax.com are almost always unregistered (or cheap to buy). They're far more memorable and brandable than the alternative you're considering.
2. Who are your customers? If your business is consumer-focused, I'd probably try to find a .com. B2B or to tech-savvy people, on the other hand, probably wouldn't mind GetXApp.com.