Ubuntu One Significantly Slower than DropBox
Please understand that Ubuntu One is a relatively new service compared with Dropbox. A lot of effort has been put in to integration and easiness of use for the end users.
These are normal things to sort out in the close future. I do not believe that there is something actually wrong with any configuration and will gradually improve with time and further releases of the software.
Dropbox will not always re-upload a file. It will first analyze the file (md5-check I think) and if you or another user already has the file on the server it will use that one instead. They said so in their blog (check the part that says Data Practices).
Note that this was also the reason for some security problems they had, as a hack allowed users to "upload" files they never had in the first place.
If you want to make a direct comparison of upload speeds, I suggest you use unique files, such as a truecrypt container with a long encryption key.
There are two possibilities for the speed difference, both worth investigating:
Dropbox uses deduplication extensively (both within and between accounts). By using an rsync like checksum method, they can identify data that they already have, and therefore don't need to upload. This will give the "impression" of a faster upload. One way to check this is to upload some NEW guaranteed unique files that defeats the dedupe mechanism (encrypted files should work).
Dropbox uses a hub and spoke architecture (for connecting with the Dropbox servers that handle the metadata, and the Amazon S3 servers that handle the data). However, under certain circumstances, it can also switch to a peer to peer transfer within a subnet. Available bandwidth between computers on the same subnet is far greater than between the subnet and the internet servers at S3, giving the illusion of different upload performance. Try having your different machines in a different (IP) location, this may defeat the p2p mechanism (unless Dropbox is smarter than I think they are).