Anything that gets offered unlimited on the internet has a Fair Use policy attached to it. Actually it means there are limits, but they are just not specified. You might be disappointed the service you receive is not as unlimited as advertised, but it's also to assure the perfomance of your site and the others that are on the same shared server box. So actually it's a good thing it's not really unlimited.

The only way to know the limits is to exceed it and receive a warning. We received one and want to share it with you, so you know what this limit is before exceeding it.This is useful because the trigger of a warning is three times higher as the limit they force you to go back to if you exceed it (EDIT: Not true anymore. BH has set the trigger on the actual 1000 table limit).

The limit (to get a warning) is 1000 MySQL tables or 3 GB of database space, excluded the Information scheme that takes up 34 tables. A minimum Drupal 6 install has already 47 tables, but for an average Drupal site (contributed modules installed) this is 2 or 3 times that. Calculate a space of 150 tables + 33% for each site (some margin + tables for email addresses), so 200 tables. This amount of tables would also be in  the critical zone of slowing down your site's performance too much. 1000 divided 200 equals 5. Sure, if you have high traffic sites and video content on your server, it would be wise to keep it lower. Using Drupal, the  the 3 gig of space is much less an issue (at least if you clear your cache once in a while) than the allowed number of tables. Five Drupal sites on a Bluehost account is a decent number. It assures you good performance and keeps the cost per site within reasonable limits even if you host a few sites for family and friends.

Consider also the maximum amount of files of 200.000. Don't exagerate having many different  image preset sizes cached, multiplying each photo several times. Better to use third-party sites like Picasa and Flickr to host your images elsewhere. The latter service even provides an embedded code for a neat slideshow of a complete set (album). Embedded videos from YouTube saves a lot on the CPU resources when multiple user are watching your vids.

To know your situation

• File count (<200.000): Find them in the left sidebar stats of the cPanel mainpage. If you want to see the bottleneck, click on the link to the File Count page under it.
• Table count (<1000): In the main panel from phpMyAdmin you open the first tab Databases and click Enable Statistics at the bottom. See the bottom of the Tables column.
• MySQL space (<3GB): In the same table look at the bottom of the Total column. To find the bottleneck, see what database takes up most space and open it by clicking on the name in the Database column. In the page with the single database tables, click on the column title Size to see the biggest on top. Probably it's a cache table that you can empty (truncate) without any problems (at least in Drupal you can) by clicking the trashcan icon.

The Pro account

Recently BH started to offer a Pro account to their existing customers. It says "Increased CPU and Memory" but it's not specified, so we asked. They reply:
* 2000 Max Emails/Hour (up from 750)
* 5 GB Total MySQL Databases (up from 3 GB)
* 5 GB Single Database Size (up from 2 GB)
* 3000 Database Tables (up from 1000). Based on the calculation above you can conclude it's feasible to have at least 15 independent Drupal websites running under one Pro account, using one mail Roundcube install for all (and of course no other installs).
* 15 Mb/s Bandwidth (up from 8 Mb/s)
* 10 Gig Total PostgresSQL Dtabases (up from 3 GB)

We add from subsequent information in Live chat with BH (thumbs up) that the file count is the same as on a normal account, namely 200.000, which is still a higher amount compared with most other hosters. We are still a bit in the dark for the Increased CPU bit, but never ran into limitations on that point yet resulting in a website being down. We guess our sites simply don't have enough visitors contemporarily  to invoke that.

For us it wasn't clear if the $20 was to be added or if it substitutes the actual monthly fee. It substitutes it. BH calculates a new year from the moment you upgrade, minus the fee you have paid till your account expires. Nice and precise.

We are trying it now and the loading of our more complex webpages is a lot quicker, allthough We didn't measure it objectively. Notice that it's an offer. In a year you will be paying around $25 a month. Also consider that now a 20% tax is added, also for the foreign accounts. This wasn't the case a while ago, but due to US legislation.

Notice also it's performant for now. As more people switch to a Pro account, the boxes for the Pro accounts will get busier. We think it is not a VPS or cloud (yet), although the price comes close. And also, cloud computing isn't a magic way to scale a website. Let's stay critical and see what happens. In the end, what counts is the performance for our visitors and for us the possibilty to configure or access things how we want to. How that's done is up to BH. For now you can consider us a very happy BH customer (thumbs up for the support team and the Live Chat function).

Note: The numbers mentioned are based on our personal experiences we have on our BH accounts and decline any liability if this or any other info here is incorrect now or in the future. For exact numbers and future tendencies, please refer with BH.