Mark,
I bought one of the CaddieUp Tandem bikes off of eBay. For the money it isn't a bad deal at all. However be prepared to dump some money into it on better components. I replaced all the cranks, stem, front handlebars, pedals, seats, and tires. I wanted to make the bike rideable for my wife and myself so Nashbar got a lot of business along with eBay. Here is why I did what I did.
1. I replaced the chain tensioner wheel bolt with a stainless steel bolt and nuts from the local hardware store. The other would bend and not stay on well. This turned out to work well.
2. The cranks that came with the bike were absolute junk. I just bought standard non tandem cranks off of eBay and put them on. The timing side uses a single 44 tooth wheel. Because three of the cranks will be threaded incorrectly you will need to get some red loctite to keep them from unscrewing. Even with the standard equipment cranks you will need to do this. I have not had a problem with the loctite...it works great keeping the pedals on.
3. The stem was junk and was bent. I wanted more rise so I put on a Kalloy adjustable stem.
4. I didn't like the handlebars that came with it so I replaced them with a cheap $10 bar from Nashbar. There was nothing wrong with the bar...just a personal choice.
5. The pedals that came with the bike are plastic junk. I bought some clip pedals from the front cranks and reversed the clips so they would work going on backwards (see about on the thread problems). My wife on the back likes standard BMX platform pedals. I had to purchase two sets of those because one thread is backwards, and one is correct. So I ended up using the right pedals from two sets.
6. I found the seats uncomfortable. They might be fine for you. I bought two matching seats off of Nashbar.
7. The tires are fine that come up with it. I purchased some cheap wide Bell slicks from WalMart at $10 a piece. I just wanted a smooth wide road type tire to cut down rolling resistance.
8. I peeled all the CaddieUp stickers off the bike. The stickers make it look like junk. It looks a lot more custom now.
Results: It was a pretty nice bike for the money. I have less then $400 in the bike and it can go pretty well. I have taken it out and can get it going pretty fast. The bike is not light, however it is pretty strong. I am around 300lbs, and my wife is 150lbs. It seems to handle our weight just fine. I say go for it as long as you understand that what you get won't be totally what you want...and your willing to invest a bit to get it the way you want it.
Cliff