There will be issues. Adobe has listed issues on CS 5.5 (works mostly) and CS 2 (won't work at all). A more detailed listing is not yet available. If you want to install Lion and use CS 3, your best bet is to use a test machine as you are guarenteed to have problems. The only questions is how many and how bad. If you cannot afford a test machine or an external hard drive, you cannot afford Lion, since if your business goes down a recovery may take an extended time.
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