1. Number of CPUs supported
SQL Server Express uses only one CPU at a time.
It can be installed on a server with multiple CPUs, but it will use only one CPU at a time.
2. Maximum memory used
SQL Server Express uses a maximum of 1 GB memory for it's data buffer.
So, if your server has severaql GB memeory, SQL Server Express cannot take advantage of it.
4. Database size limit
Maximum database size is limited to 4 GB (log file size is not counted)
5. Profiler in SQL Server Express
Profiler tool is not included with SQL Server Express editions.
6. Job Scheduler
Job Scheduling service is not available with SQL Server Express.
7. Import/Export
Data import and export feature is not available with SQL Server Express.
Source:
http://www.dotnetspider.com/tutorials/sqlserver-tutorial-158.aspx