There are always indirect limits, and any host retains the right to terminate or suspend accounts that threaten the server's stability. Generally speaking, the more you pay, the more you can expect from the host.
User may not:
Use 25% or more of system resources for longer than 90 seconds. There are numerous activities that could cause such problems; these include: CGI scripts, FTP, PHP, HTTP, etc.
Run stand-alone, unattended server-side processes at any point in time on the server. This includes any and all daemons, such as IRCD.
Run any type of web spider or indexer (including Google Cash / AdSpy) on shared servers.
Run any software that interfaces with an IRC (Internet Relay Chat) network.
Run any bit torrent application, tracker, or client. You may link to legal torrents off-site, but may not host or store them on our shared servers.
Participate in any file-sharing/peer-to-peer activities
Run any gaming servers such as counter-strike, half-life, battlefield1942, etc
Run cron entries with intervals of less than 15 minutes
When using PHP include functions for including a local file, include the local file rather than the URL. Instead of include("http://yourdomain.com/include.php") use include("include.php")
While our shared services are suitable for the bulk of our customers, there comes a time for some websites when they are better suited for a larger plan, which allows for more dedicated CPU and memory resources. We reserve the right, in our sole discretion, to discontinue service to any customer with a website or other hosted data that takes up more than 10% of the server resources and/or 10% of the server's CPU. This means that if your website is found to be utilizing more than 10% of the CPU and memory of the service, we reserve the right to take your site offline. If this becomes necessary, you can either upgrade your hosting package, or request a pro-rated refund of the amounts you have paid in advance for the services. Due to the severity of this, and our ability to act quickly to correct these situations to avoid server issues, we will do everything reasonably feasible to provide you with a warning prior to taking your site offline, but we accept no obligation to do so.
The use of more than 50,000 inodes on any shared account may potentially result in suspension. Accounts found to be exceeding the 50,000 inode limit will automatically be removed from our backup system to avoid overusage. Every file (a webpage, image file, email, etc) on your account uses up 1 inode. Sites that slightly exceed our inode limits are unlikely to be suspended; however, accounts that constantly create and delete large numbers of files on a regular basis, have hundreds of thousands of files, or cause file system damage may be flagged for review and/or suspension. Over time, tens of thousands of messages (or more) build up, eventually pushing the account past our inode limit. To disable your default mailbox, login to cPanel and choose "Mail", then "Default Address", "Set Default Address", and then type in: :fail: No such user here
Quoted from http://www.justhost.com/terms-and-conditions
That being said, their hosting has been a nice surprise, better than what I had expected based on customer reports I've read.