Last year, for the first time, we decided to pay for SDL technical support.
We did this mainly because the maintenance agreement includes the upgrade to the next major version - we calculated that by upgrading all our licenses to the current version by the April 15 deadline for the discount pricing, and by paying at the same time for the one-year maintenance agreement, we would get Trados 2009 at a convenient price.
So far the quality of paid support has been generally good: accurate and quick response in helping with the installation and licensing of the various components, good suggestions (in general) about how to overcome certain problems (e.g., the suggestion about how to use Trados 2007 with Office 2010), some less than good suggestions (suggesting that in order to speed up downloads one should disable firewall and antivirus is not what I would call a good idea), and one thing we really appreciate: almost all our support tickets are apparently handled by the same person, so we don't have to explain everything again every time we open a ticket (tellingly, it was not our favorite support person who suggested we disable antivirus and firewall to speed up the download).
Things that I find should be improved: the web interface for entering support tickets is overcrowded and clunky. The quality of the articles in the knowledge base seems to be hit or miss: there are many helpful articles, but my impression is that a non-technical user would be at a loss.
Overall, I would give SDL tech support a B+ grade (higher than the grade I would give to SDL's software, as a matter of fact)