Ok,
I've just spent the last 24+ hours trying to download three freaking files. First I tried direct with firefox. Got to 98% and then said that the source couldn't be read and aborted. When I tried to retry it wanted to start over. It had taken hours because the download was only going at 60-80KBps on a 4Mbit DSL.
I said fine, I'll try in download manager (wxDownload), it got 250KBps and was doing great... for 10 minutes. Then gog.com (actually their mirror in San Fran bitgravity) started aborting my downloads and giving me 403 forbidden errors. So I tried AGAIN, this time using 1 stream only. Same thing after about 20-30 minutes.
So finally I tried gog.com downloader. This got to 88% and then gave me some lame error and said "sorry" then it removed the game from the queue. Again, when I re-added it, the download went to 0%.
I've sent two support tickets over the last two days and got no response. Guess they don't work or have any staff for weekends. And before anyone says it, yes I set it and go to bed. Problems is without babysitting it, the download aborts in a few minutes and the server starts giving me 403 forbidden errors. When I then have to log into the site, and click the link again to get a different source address.
But this isn't the first time it happened. I also bought a game several months ago and had problems with downloading. I had to download the files several times because of CRC errors from installer. Even on the 2mb part ones. I've since moved across the country and live less than 300 miles from the host servers. Still having problems with them.
Is it just me or does their download horribly suck?
P.S. Yes I'm ranting, I wasted a weekend trying to download something that should have been done in an evening.

Yes, indeed they do. I take it you are using a download manager? All good download managers allow you to feed in a new source URL. GOG's servers support resume, so once a new source is provided the download manager should just pick up from there without losing any progress. Download managers typically discard the last few chunks to ensure the loss of connectivity didn't result in some broken chunks being added to the file (which would make the whole thing faulty), but this is only ever an insignificant portion of the total download size and won't noticeably increase the overall download time.
It could be that using more than one segment is messing up the server's authentication process and/or timeout delay; I have had no problems downloading at my connection's full speed (with minor fluctuation) with only one segment, and I'm in New Zealand.

Yes, the download manager I was using supported additional source links. But that didn't help as the file was corrupt in the end. (After having to resume it with about 30 new links. I did also try to set it to once part/stream. No help their either.
I'm back using gog.com's downloader and it resets back to 0% after the error.
UPDATE:
I tried two more times today. Again, gog.com's download manager failed. After about 15 resume attempts with new URLs each time I got the larger file. Just got it installed. Hope it's okay, but still have another game to try and download. Given the current track record I'm looking at a week to download.

Actually, if your traceroute stopped somewhere in your city, it sounds to me like your ISP is doing some kind of filtering that is interfering with your downloads, most likely something that is meant to restrict large file sharing. It still doesn't sound like a GOG issue to me, since if it were, more of us would be encountering the same issues.

^I concur.

I've never had any problems and concistently download at about 2.5 MBytes/s per file when getting 3 or less files at a time (yes, bytes, not bits). I'm not clogging up the pipes at the moment though as I'm not at home and thus don't have the speedy line.

Or it could be that there is a router that is fubar.
But I didn't get the impression that the trace route skipped any hops. I'm thinking it goto to exactly where it had to go and he deduced that it is in the same city as him.
In terms of your suggestion though...
What ISP are you using linuxkernel?

wow. im lucky then.
always constant 100kb+ (but i have other stuff running which eat my bandwidth)
never had a problem.

As some of you know by my complaining (grrr telstra grrr) in various places, most of the time, I'm stuck at thirty kilobytes per second. So slow, I need to spell it all out.
No real issues with downloads though, aside from the rare known glitches: part0 files on 'complete' status, and downloaded complete *.bins vanishing if you cancel(or service cuts out) on an uncompleted download as part of the pack. (probably a better way I can word that...)

Final update:
I did get the game installed. For a single 2GB file it took days to download with much babysitting. I didn't have problems with the downloader (not gog.com but wxDownload) deleting it when I got errors. Just got CRC issues on the completed file.
The final download took several hours and I had to keep feeding it fresh links every 5-10 minutes. This process was tedious to say the least.
I know this is a classic response, but every other site worked with 250-350KBps without problems. Speed testing my connections shows 3-4Mbits. Even bitgravity network debug showed 2.4Mbits. Which is much less than 30KBps I was getting. I did a complete workup with Peter from support on it this and more. However, I'll be leaving the country soon so won't be able to test further from here.
And forgot to mention, I tried all 4 bitgravity mirrors. (bitcast-a through bitcast-d)
Same problems, although they are very different subnets.
The only good news is I did finally get the games... not sure I'd want to go through all that again though.