I know this is the manuals section, but this seems to be a hot topic and also there seems to be confusion. Here is my take.http://dri.freedesktop.org/wiki/DRM/http://dri.freedesktop.org/wiki/glxinfo
To check for hardware acceleration simply:
glxinfo | grep render
(see the second link above to interpret the output.) To install mesa-utils:
apt-get install mesa-utils
This is just an application/utility to look at driver status and has nothing to do with whether or not the system is using hardware acceleration. (AFAIK)
**Downgrading Mesa is only necessary if you have a really old card. http://www.phoronix.com/scan.php?page=news_item&px=OTgzMg
How to downgrade: https://wiki.ubuntu.com/PowerPCKnownIssues
There are several issues that can cause DRI to fail.
1. Make sure you don't have it turned off in your xorg.conf.
2. Multiple graphics cards (which can be mimicked by framebuffer conflict--Thanks Rsavage for helping me understand that)
3. You must use a driver that supports it. FBDEV and NV do NOT. Look at /var/log/Xorg.0.log.
4. Missing microcode or firmware. http://wiki.debian.org/AtiHowTo
These statements are made with no warranty or claim to accuracy.