I tend to upgrade about every 3 years, as do my clients (I keep the older versions, just in case). I would purchase 2011 for now, as the diff between 2010 and 2011 is minimal so I 'spect the diff between 2011 and 2012 will be as well. The diff between 2008 and 2010 is ridiculous, and QB no longer supports 2008, anyway. This will give you a chance to learn the newest bells/whistles in QB 2011.
If you are offering services for clients, under no circumstances should you expect them to pay for the software unless it is proprietary to their company.
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