Very interesting; try downloading a file from your Dropbox public folder via HTTP, and see if that's any faster. If it is, your ISP is probably throttling/QoSing Dropbox, the ports it uses, or the kind of traffic it generates specifically, and you should get in touch with them about it. If it's slow as well, your ISP might be having a peering problem to Dropbox's colo.
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By the way I just ran this speed test:
http://www.dslreports.com/speedtest?flash=1
My network downloads 4MB/sec
The computer has a fresh install of snow leopard and everything else is fast.
Very interesting; try downloading a file from your Dropbox public folder via HTTP, and see if that's any faster. If it is, your ISP is probably throttling/QoSing Dropbox, the ports it uses, or the kind of traffic it generates specifically, and you should get in touch with them about it. If it's slow as well, your ISP might be having a peering problem to Dropbox's colo.