Quite simply, Sales Cloud is more geared towards business development and Service Cloud is geared towards Call Centres, Live Agents, PABX integration etc
In Brief:
\”Sales Cloud\” refers to the \”sales\” module in salesforce.com. It includes Leads, Accounts, Contacts, Contracts, Opportunities, Products, Pricebooks, Quotes, and Campaigns (limits apply). It includes features such as Web-to-lead to support online lead capture, with auto-response rules. It is designed to be a start-to-end setup for the entire sales process; you use this to help generate revenue.
\”Service Cloud\” refers to the \”service\” (as in \”customer service\”) module in salesforce.com. It includes Accounts, Contacts, Cases, and Solutions. It also encompasses features such as the Public Knowledge Base, Web-to-case, Call Center, and the Self-Service Portal, as well as customer service automation (e.g. escalation rules, assignment rules). It is designed to allow you to support past, current, and future clients\’ requests for assistance with a product, service, billing, etcetra; you use this to help make people happy.
The differences between Sales Cloud and Service Cloud are the same across each \”edition\” (\”professional\”, \”enterprise\” and \”unlimited\”), mainly outlined above. The differences, as you can gather from the prior paragraphs, is that each cloud is designed to support a specific set of features that you would use to sell services and products, and support those services and products (respectively).
The main differences you will find are the limits between each edition. Professional Edition provides basic functionality; you can create limited customized UI pages (Visualforce), and you can use standard automation (e.g. assignment, escalation, and auto-response rules). Enterprise Edition provides additional features, including custom automation (e.g. workflow rules, Apex Code), improved Visualforce functionality, integration (API) access, generally increased limits, and additional customization features (e.g. more fields per object). Unlimited Edition is an extension of Enterprise Edition, and includes more storage space, premier support, more objects, increased API limits, and so on.
Cheers!!