The first thing to decide is whether you want to be able to read your DRM-infested Adobe e-books or not. If you write them off (i.e. only read them on your laptop from now on), then the PRS-500 may be salvageable.
If you want to read your Adobe e-books on a pocket-able device, then a Palm is your only choice. See for example
Secure Adobe Reader 6.0 at FictionWise. It says that Palm devices can read their Secure Adobe content, but I would check to make sure your exact model number is supported on your e-books (e.g. ask at where ever you bought them from). You can read other e-book formats on a Palm, so it is a reasonable choice (if perhaps a less clearcut win over Windows Mobile devices than it used to be).
If you never want to get in the DRM lock-in trap again, and have a Windows laptop, then one option is to only buy non-DRM (typically multi-format) e-books or "secure" .LIT (MS Reader) e-books. The .LIT DRM can be stripped (e.g. using CovertLIT or ABC Amber LIT Converter) and the file can then be converted to whatever format you want. One option is lit2prs for your Sony, see
libprs500 now includes MS LIT converter: lit2lrf. Note that the legality of stripping DRM is at best a gray area in some countries, but is victim-less if you bought the original e-book and don't give it to anyone else.
If the ConvertLIT route isn't for you, but you still want to buy DRMed e-books, then switch to MobiPocket. It is widely available, and its DRM can be broken if circumstances change in the future.
One last point is that Adobe Digital Editions should eventually be able to read your Adobe e-books (if it can't already). Adobe DE will be available on the Sony PRS-505 next year. My betting is that it won't be available on the PRS-500, but Sony has not said for sure one way or the other that I have heard.
I personally regard Adobe as the only "evil" e-book vendor. They and their content providers have a history of screwing their customers. I'm sure what they do is legal (i.e. you got what the fine print said you were buying), but they are not an ethical company that looks out for their customers (hence "evil"). There seem to be more support issues with Adobe e-books than with other formats, and if you read the FAQs of some of the sellers of both Adobe e-books and other formats you get the impression that they are quite fed up with Adobe too. In its favor - it is one of the few e-book formats available from libraries (MobiPocket is another).