Been dominating with TB recently, but am curious how others have been playing him, especially hybridized.  Here's my first 10:

Fireball 1

Circle of Ice 1

Deep Freeze 1

Fireball 2

Frost Nova 1

Circle of Ice 2

Fireball 3

Circle of Ice 3

(Save point)

Fireball 4 and Frost Nova 2

Favor: Blood of the Fallen

first 1000 Gold:

Scaled Helm + Sundries (Flag lock, teleport, revelation totem, all depending on map and team. Healing pot possible too).

Next 6000 gold

Journeyman's Treads

Nimoth's Chestplate

Vlemish FaceGuard

~Hauberk of Life, MAYBE the Plenor Battlecrown

So, first up I think fireball is a vastly superior spell to get at level 1.  You don't creep as fast, but repeated hitting with fireball can chase people from lane.  In general, even if you get Circle of Frost at level 2, you shouldn't use it much at all.  Save your mana so you can just keep the fiery pressure on the opponents. Over the course of about 30 seconds to a minute, a level 1-3 TB can keep an upper hand on most opponents.

I go for Frost nova big time, as it is a fairly fast interrupt, that also let's your team get the drop on someone. It also very strongly helps your team attack defended points (Left and right sides on cataract, to capture gold mine and/or portal flag).

Circle of Frost becomes better once you get it to level 2, as it does whipe out a full wave of creeps. That said, I still suggest not overusing it. There is nothing as sad as a TB with no mana.

Other general strategies: Try to keep both transform bonus' going at all times, especially the mana boost. TB's level 1 mana regen is pretty respectable with the Helm, and his primary fireball skill is very mana efficient, but still, when push comes to shove, you want to have the mana to have nova, fireball, rain, and Deep freeze all at your finger tips.  The difference between having and not having these is much bigger than a little extra gold from a lane.

I generally start confrontations in Fire, to lead with a fireball, and then switch to frost to persue or interrupt (Both deep freeze and nova work here). Get a good feeling for when to switch back to firemode to drop another ball.

Notice that most of my gear is HP based.  TB dishes out a lot of damage, and is one of the few DG's who well and truly ignores armor. The amount of attack damage you do in a game is pretty small, because you don't 'just attack' too often.

Keep an eye out for teammates.  Since you do a lot of burst damage, and have a strong control suite, teleporting in to finish someone, or getting behind them, can be clutch.

The one area I'm still trying to figure out, is in levels 11 through 15.  My natural inclination is to just get the last point in circle of frost, and then tech up deep freeze for the fireball buff.  Thing is though, that I often do not GET to level 15 in a game, and am basically wasting mana/points on getting more Deep freeze. 

Has anyone had any success with the auras?  I'm not even sure what numbers they post, but a little Area slow (Ice is your persuit form, I can't imagine changing to fire until I'm ready to Ball) sounds nice.