Can't see Macbook WiFi access point on Android smartphone
In Snow Leopard (sorry, I don't have a Lion to try this with):

In System Preferences > Sharing, 


Enable 'Internet Sharing'
Enable 'To computers using AirPort'
Click the 'Airport Options' button and set up hotspot's network name and encryption. The AirPort will have to be off for this button to be active.
'Ok' to back out to the Sharing pref pane.


On the Network Preference Pane, or on the menu bar,


Turn on the AirPort.


Your device should see your Mac as a WiFi access point.