I went there in october 07. There was a hurricane south of us, so the beach waves were really rough. A lot of spikey puffer fish. Maybe they are usually further out at sea, but there were 100s of them on the beach because of the curent. A couple of guys on the beachwere having a "mexican snowball fight" with them. It was pretty funny, if not a bit gross. the wind was so bad, we decided to go back into town.
The town is a quant seaside town. A big problem is they were not able to handle the large influx of tourists that the boat leaves there for one day. Most restaurants you had to wait a long time because there were not enough dishware to handle the amount of customers.
When we got off the boat, there was a hive of bees there to greet us (yes, I know, not La Paz' fault).
The really bad thing that happened to us was that we were traveling with some good friends. They are an African American family. When we finally chose a restaurant that looked like it could handle the crowd, the waiters and waitresses did everything possible to avoid our table. It was pretty obvious why. I probably shouldn't go into any further detail.
A table mate of ours on the trip took a taxi that day from the beach to the town. The cabbie proceeded to tell them that he thought the Carnival was crazy for using La Paz' port as a stop. Most of the sea-based cocaine trafficking from Columbia that gets into California gets pushed through Baja from that very seaport. He said there are some very bad people around. Keep in mind, we saw nothing of this.
My suggestion - get off the boat mid morning (10ish), shop a bit, maybe have an ice cream or something, then get back on the boat for a late lunch and spend the rest of the day poolside on the lido deck.
When we went, a large group of Carnival employees were doing "test runs" of various excursions they planned to provide at a later date. If these are available, consider them.
Matt