I concur with gertrude on the uplink speed, most broadband suppliers are 128k or 256k upload which is more than sufficient as typical use sees the user download multiples more than they upload.
Whilst having a higher upload speed may help the odd time you need it - it comes as a sacrifice of the download speeds. Using a dedicated line like a T1/E1 you will get a 1.5/2 mbps pipe but that means whilst uploading at 1mbps the remainder of the pipe is available for download.
The same principle applies to broadband - if your broadband line is capable of 8mbps and you have 1mbps upload speed your effective download speed will be 7mbps.
This is also true with WIMAX whereby there is a dedicated bandwidth fequency spectrum - if part is used for upload only the remainder can be used for download.
The above is one reason the upload is throttled, SDSL as you may read about is where the bandwidth capability is split half and half between upload and download - this makes the service more pratical for serving to the internet - e.g. web servers which is why it costs alot more and is focused at businesses (these products compete with leased lines such as a T1/E1.
Cheers
Jof
p.s. T1 is a 1.5mbps (24 64k channels) dedicated leased line as found in the USA, an E1 is the european equivalent which is 2mbps (32 64k Channels).