ESRI has added some very useful functionality for exporting to Adobe PDF. Not only can you turn layers on and off, you can also do an "identify" and a "find" on any data in the layers and extract the Latitude and Longitude from any point on the map while in Adobe Reader. For these advanced functions, you need ArcGIS 9.3.1 and Adobe Reader 9 or later.

When you export a map, first be sure to look at all the options. For example, be sure to check "Embed all document fonts" when exporting to PDF to be sure that all your fancy symbols are exported correctly and will print properly.
To add more viewing choices and query abilities, click on the Advanced tab and select Export PDF Layers and Feature Attributes. Also make sure that Export Map Georeference Information is checked. If you have a lot of tables with many fields, you can improve performance by turning off all unnecessary fields.

To turn on the table of contents in Adobe Reader, just click the layers symbol and you can then turn all the ArcMap layers including annotation, on or off separately. However, if you have any raster layers or layers with transparency, they will be lumped into one layer.
To access the "identify" and georeference functions select Tools>Analysis. To use the Object Data tool, click the object you

want to identify 3 times. (Remember Dorothy in the Wizard of Oz?) The first click highlights the map; the 2nd click, the layer; and the 3rd click, the object you want, opening a dialog box with all the attribute data.

The data for that object will now be showing on the left-hand side of Adobe Reader in the Model Tree. You can also select features from the Model Tree and they will be highlighted in the PDF document. If you want to know the Lat/Long, just move the Georeferencing tool to a place. If you want to search the database, just type a word into the Find box at the top of the PDF. For example, typing in "rest" would select all the restaurants in Mahahual.
Using these advanced functions is a way to make your exported PDF files much more dynamic and useful for others and is a good way to share data with people that don't have ArcMap. One drawback to this is that symbology is not scalable in Adobe Reader, so simpler symbols and smaller areas work best.