Views 3 provides solution for your question from the box. It's the Global: Combine fields
filter.
Add fields
Add
Global: Combine fields
filter to filter criteriaCheck fields you want to combine in filter's settings
If you use Display suite or teasers mode - force using fields in the View setting.
Solution 2
Views filters populate - good module. But there is 1 problem "only populates STRING exposed filters".
For more info, refer to the Views issue about Apply One Exposed Filter to Multiple Fields.