As a right, you can purchase a Raspberry Pi and use it for what ever intended purpose that you desire.
However, the major problem that you could run into is the level of availability. RPi's are hot little devices with limited availability. Demand will certainly cool off in the near future but even in regards to a longer time frame (a year or two) production capacity may not be be wide enough to fill larger quantity orders (1000+) for commercial applications.
Long term, this may be a possibility but for the foreseeable future the RPi may not be your best choice for an embedded commercial computer system unless you are expecting to integrate the device in a very very small number of units and you are willing to wait a long time to receive your own inventory.
Only you know your specific needs and can justify the use of the device.
Yesterday (July 16, 2012), the official Raspberry Pi blog released information stating that production of the RPi boards is being significantly ramped up and that purchase orders should be filled within 4 to 6 week lead times and bulk orders of the device can now be placed.
Of course, if you need an excessively large number of units (i.e. multi-thousand), receiving your Pis may take more time than the alloted 4-6 weeks. Additionally, Gizmodo has reported that production has been ramped up to 4,000 units per day. I believe that for most cases this production quantity should meet the demand of most small to mid-sized projects.