I need Linux hosting services, preferably based in USA and which have been in business at least for 2 years.
I have found pacifichost.com and it offers unlimited domain webhosting plans.
How good are they? Do you think that I can trust them?

I recommend you have VPS for that https://www.pinellashosting.com/portal/cart.php?gid=5
I have been with them for some time and I think you won't regret once you try them

You'd better search for more information from different hosting companies and make great comparison to select what you like the most.

Hello

• I happen to have one such plan with unlimited number of domains. I find it extremely convenient to access my six websites from one control panel with central administrative functions. I am able to create new email IDs for three of my websites with this control panel if there's a need. I can add different applications to different websites without leaving the single control panel.
  
  As my plan can accommodate numerous domains, I am able to access the server directories of all my websites through FTP with one single login. This is saves me much time, because if I want to add some images to 2 – 3 websites, I can do it very fast than individual logins 2 – 3 times, once for each website.
  
  
• When your web hosting company is reliable and offers hosting with unlimited domains, it means that you can be rest assured that all your websites will be looked after with the same level of professional service.
  
  If your web hosting provider has an admirably long uptime, it means that all your websites stand to gain through that feature. When your different domains are hosted on various servers, it may increase your chances of having downtimes, as some servers are more likely to experience some problems.

Hosting

yup i agree with Buck, maybe you better need more informations from different hosting provider, like kvchosting, or many other hosting company.
hopefully you get the best.

I have seen mostly positive reviews on pacifichost. Seems to be good and decent company

I cannot say anything about the asked host, but if you need an unlimited domain hosting plans I may give serveral recommendations.

Try looking through such companies as webhostgiant.com (american) and santrex.net (offshore) which are offeirng low cost but highly stable service being experienced and stable hosting providers.

I have seen attractive unlimited plan at $4.77 per month after 40% discount with coupon eggnog.
That's the offer from a2hosting.
They are trustworthy and have stable servers which are administrated for 24 hours.

I recommend one of these: webhostingtable.com

Powweb has the best offer right now. It's on a 50% sale - $3.88/month ($46.56/year), and you get a free domain from them.
Their hosting plan includes web builder, so you can create your site just by drag and drop (without any programming), or you could install Word Press (easy, one click install from their control panel), choose a theme that you like, and start adding content.