I bit the bullet and upgraded to CS5 from CS3; however, I won't be buying anymore Adobe products in the foreseeable. In particular, I won't be buying anything that requires a seriously overpriced, unfriendly to the end-user subscription. Sadly, Adobe has gotten too big, too unwieldy, and too expensive. After playing around with Muse for a couple of hours this morning, I think Muse is a product that's symptomatic of much bigger problems with Adobe's current business model; that is, overpriced, underwhelming, and based on hazy/lazy assumptions about what its users want/need.
I will continue using CS5 for the time being, but I've already started looking for alternative software to replace it--and high quality, user-friendly, alternatives that don't break the bank are easy to find by anyone willing to spend the time looking.
Unless Adobe wakes up and starts paying close attention to what its users are saying, it will find itself on the fast track to being about as relevant as Microsoft has become of late.