While browsing Sharepoint newsgroups, I found a very useful reply from Eddy Blanco which provides excellent information to estimate your SharePoint site and structure. Following is the information, all credit goes to Eddy Blanco:
| SharePoint Area of Interest | Optimum Size |
| Site collection | 50,000 per Web application |
| Web site | 250,000 per site collection |
| Subsite | 2,000 per Web site |
| Document | 5 million per library |
| Item | 2,000 per view |
| Document file size | 50MB (2GB max*) |
| List | 2,000 per Web site |
| Field type | 256 per list |
| Column | 2,000 per document library 4,096 per list |
| Web Part | 50 per page |
| Users in groups | 2 million per Web site |
| User profile | 5 million per farm |
| Security principal | 2,000 per Web site |
| Search indexes | One per SSP, Maximum of 20 per farm |
| Indexed documents | 50,000,000 per content index |
| Content sources | 500 per SSP |
| Start Addresses | 500 per content source |
| Alerts | 1,000,000 per SSP |
| Scopes | 200 per site |
| Display groups | 25 per site |
| Crawl rules | 10,000 per SSP |
| Keywords | 15,000 per site |
| Crawled properties | 500,000 per SSP |
| Managed properties | 100,000 per SSP |
| Authoritative pages | 200 per relevance level |
| Results removal | 100 |
| Crawl logs | 50,000,000 |
| Shared Services Provider (SSP) | 3 per farm (20 per farm maximum) |
| Zone | 5 per farm |
| Web application | 99 per SSP |
| Internet Information Services (IIS) application pool | 8 per Web server |
| Site collection | 50,000 per Web application |
| Content database | 100 per Web application |
| Site collection | 50,000 per database |
| Index servers | 1 per SSP* |
| Application servers running Excel Calculation Services | No limit |
| Query servers | No limit |
| Web server/database server ratio | 8 Web servers per database server |
| Web server/domain controller ratio | 3 Web servers per domain |
