I know the rules for TFD in 3.5 mention it can carry anything within its weight limit and can be directed by the caster within its range limits, but are there any rules about actually riding Tenser's Disk? I realize the capabilities implications of travel by hovering disk would probably be DM's call, but in general what's the consensus on using the TFD for self-transport?
No, you can not ride a Tenser's Floating Disk.
There is a definitive, and official answer from the WoTC 3.5 FAQ (Pg. 91);
Can you ride your own Tenser’s floating disk?
No. While you could command your Tenser’s floating disk to move close enough for you to sit upon it, it has no ability to move under its own power. It can follow you only at a maximum rate equal to your normal speed.
I would not say that being able to ride the disk is game-breaking or overpowered. Another first level spell exists called Mount that is comparable to Tenser's floating disk. Depending on your need, maybe better. It is also a first level wizard spell. There is nothign to stop you from loading up your mount with jewels or gear, like you would a Floating Disk. You can also compare it to the spell Levitate, which is a second level spell that allows you to float 20-ft. from the ground. There exists a 4th level spell called Greater Floating Disk (Spell Compendium, Pg. 96) which has a fly-speed of 20-ft. and specifically says in the spell description that it allows characters to sit on it and ride it.
You could certainly ride it, it just has no propulsion of its own. So by itself, it wouldn't do much good, and certainly wouldn't be equivalent to a mount. But there are still some uses. For instance, my wizard in the Skulls and Shackles campaign (Pathfinder, but close enough) used a Floating Disk with a long pole cut from a sapling as a skiff to cross a swamp.
As others have pointed out, it has no propulsion of its own, merely following the caster around. However if you have a familiar with the share spells ability, you can cast spells with a range of self on your familiar. This includes Tenser's Floating Disk.
Because of this, cast the spell on your familiar then you can ride the disk while your familiar walks, crawls or flies around. They have to stay fairly low, but if they're fine with low flying you can get a pretty significant speed boost, as well as retaining your movement action each round by investing in a hawk familiar (60ft fly speed) or similar.