First, thanks to everyone who provided commentary on my dilemma of signing up with Flickr vs Picasa. I gave both a test drive, and really liked each. Flickr seems unbeatable for community-based features, and I have a feeling its traffic is off the charts. On the other hand, Picasa is extremely clean and straightforward in design, and the integration into Google is very handy.
In the end, though, I decided to think outside the box (as the saying goes), and signed up with Smugmug. In the beginning of this process, I knew very little about Smugmug, but after a couple days on the site, I was hooked. The design elements are really great looking, going from professional to whimsical. Customizability is outstanding, too. What sealed the deal, for me: Smugmug offers easy watermarking features, so that I can show photos that are for sale on Dreamstime, but with a watermark, and there's a handy Aperture-to-Dreamstime plug-in to make uploading simple.
I am sure all three services are great, but, even though Smugmug is $149/year, at least in the pro version, I feel good about this choice.