My wife and I spent six days on the Cloud from Tenerife to Barcelona in April 2010. By way of background, we were originally supposed to be sailing on the Shadow in the Caribbean but rearranged at the last minute due to the volcanic ash leading to our flight being cancelled so we hadn't particularly researched the specific ship or itinerary.
We are in our early 30s (so much younger than the Silversea average) and this was our first time on Silversea so I can't comment on whether standards have slipped etc.
Overall, we had an excellent time and would recommend this line/ ship to anyone. Sure, there were a few minor niggles, but nothing that would affect our decision to sail Silversea again. The only major negative was a mix up with the booking (due to our late change onto the cruise) such that there was real confusion when we arrived so that they thought we weren't even booked on the ship and then they couldn't find our cabin, but this was resolved quickly and efficiently (although our cards showed us as US and not UK citizens!) and isn't entirely surprising given the large number of changes the volcanic ash must have caused.
We had a midship veranda cabin and thought the cabin was a good size and well furnished/ equipped although the bathroom was a little tatty and could probably do with a refurb, although it was fine.
Food was on the whole very good; very varied menu and good quality ingredients in the main dining room, although a little less repetition of the same vegetables accompanying main courses would have been good. Had a meal (Burgundy menu) in Le Champagne which we thought compared favourably with Michelin star restaurants in London. We didn't have the matching wines but had an excellent bottle of red ($130) and were still given the champagne, dessert wine etc, so much better value than paying $200pp. Enjoyed La Terazza and also ate at the pool grill, room service etc. With room service, we were particularly impressed at the way that the table was formally set up, even for breakfast every day.
Used the gym, which was well equipped for the size of ship. We didn't go to much of the entertainment, although what we saw was good. We particularly enjoyed Mario in the piano bar and used to go and listen to him most nights after dinner. We also thought the cocktail choice was excellent.
As others have said, what sets this line above the average is the staff. Every need is literally anticipated before you even realise you have it. Our butler even procured a bowtie for me when mine broke just before formal night. And in the main restaurant on formal night, the sommelier (who remembered us from champagne) brought us a special wine with our foie gras. What we also enjoyed was that the staff were genuinely warm and friendly (possibly because most Silversea guests treat them with respect and therefore receive it back) rather than being subservient.
Our fellow passengers were a mixture of Americans, Brits and other Europeans. Everyone was friendly and we had some enjoyable conversations. Whilst we were the youngest guests on the cruise, we didn't feel that this affected the way anyone treated us, rather we felt that by joining the Silversea family we were automatically accepted as part of the club!
So overall, an excellent cruise, we'd definitely try Silversea again, although maybe next time on one of the slightly larger ships for some variety.