Hmm the free version is pretty slow for me aswell (couple 100 kbps) but that's normal for free accounts.
I doubt your ISP is throttling a sharing site so *shrugs* maybe you just caught some unlucky moments with overloaded servers etc.
I just reached about 600 kb/s using the Downthemall! firefox pluging, which i doubt has any effect because it's unable to open multiple datastreams downloading from something like this.
Uhmm, are your normal downloads higher? Like by how much?
The only thing i could think of is
1) you are to far away from any of the datacenters used mirroring the files (unlikely)
2) your ISP shaping traffic from and to luckyshare (very unlikely more of a torrent thing but easy testable with a free proxy)
3) your internet is just horrible, seriously horrible (the most obvious choice lol).
other then that I can't really think of anything, if your normal speed fair you could test downloading through a webproxy (just google for one) or such, if you actually get a speed increase instead of a decrease the traffic is shaped but i seriously seriously doubt that.