Editions

The msdn site Features Supported by the Editions of SQL Server 2008 shows the differences between the SQL Server editions. Regarding SSAS the Standard Edition (SE) misses the following features compared to the Enterprise Edition (EE):

Data Warehouse Scale and Performance
- Auto parallel partition processing
- Partitioned cubes
- Distributed partitioned cubes

Multi-Dimensional Analytics
- Financial aggregations
- Custom rollups
- Semi-additive measures
- Writeback dimensions
- Linked measures and dimensions
- Binary and compressed XML transport
- Account intelligence
- Perspectives
- Analysis Services shared, scalable databases

Data Mining (in this category SE is quite weak)
- Cross validation
- Models on filtered subsets of mining structure data
- Time series: custom blending between ARTXP and ARIMA models
- Time series: prediction with new data
- Unlimited concurrent data mining queries
- Advanced configuration and tuning for algorithms
- Algorithm plug-in API
- Parallel model processing
- Time series: cross-series prediction
- Unlimited attributes for association rules
- Sequence prediction
- Multiple prediction targets for naïve Bayes, neural network, and logistic regression

Of course you can build cubes without these features but they are very helpful in many situations. On the other side there's of course a difference in the licence fees... - here are some additional links to licence and pricing information:

- SQL Server 2008 Pricing
- SQL Server 2008 Licensing FAQ