I am wondering what are the advantages/drawbacks of sharing a dissertation on a specialised website (for example Social Capital Gateway). There are a number of repositories available and they seem to be more widely known. Are these sites more for the benefit of the facilitators than the contributors (who in this case are the PhD researchers).
I doubt there are any drawbacks to posting on such a site, other than the time required.
But I also doubt there are very many advantages. I don't think very many people will look on such sites for theses. If I need something from a PhD thesis, my algorithm would be something like this:
Look for published papers by the student which discuss the work.
Google the student's name and thesis title.
Look for the student's website.
Look on the department's website.
Look on the institution's library's website.
Try to contact the student (via website or Google search) and ask if they will send me a copy.
Try to contact the student's advisor and ask if they have a copy.
Contact someone else I know at the institution, and ask if they can find the thesis in their library.
Try to get a copy from UMI (last resort).
Searching other repositories would probably come somewhere between steps 8 and 9. So if you can try to make sure your thesis is findable at some earlier stage of this process, you probably don't need to bother with much more.
You should make the thesis freely available somewhere that Google will find it, and that there are no paywalls or clickwalls.
If you have a web site and you plan to keep it available, putting your Ph.D. dissertationon your web site is a perfect solution.
If you don't have a personal web site that you will keep available, then another great solution can be to "tech report it": make it available as a tech report through the institution where you graduated. Many institutions make their tech reports freely available on the web and commit to ensuring they remain available. So, that's a great solution. (If your institution doesn't make their tech reports available over the web, you might want to bug your institution to suggest they do so.)
If neither of those is applicable, a third choice can be to make your dissertation available via arxiv or some other preprint server that is appropriate for your field.
I think the question is,
sharing the dissertation on
specialised sites vs. widely known repository sites
The advantage of specialised sites is that you get experts in your discipline to read your paper. I believe that's the purpose of sharing your dissertation in the first place.
On the other hand, widely known sites would have more visitors. You would have more interested readers. Whether they are experts is another matter.
However, I would like to raise an issue here. Many sites have paywall/clickwall. In particular, many require sign-ups. I often have trouble with links provided by users on this board. I follow the link, then find out I need to sign in to read the full text. More often than not, I give up at that point. I simply don't want to sign up unless I am really interested in the article.
I truly like arXiv because I don't need to sign up to read the papers. The time I need to sign in is when I upload my papers there.
Check with your school. Legally, the work usually belongs to them (it does so here in Chile), you might not be allowed to share it freely. I doubt they will object (the school is interested in becoming known, like for your work here), but they might place some restrictions on it (say state specifically that this is your thesis at the school, cite your advisor, whatever)