Trying on black, hows it look?

While I absolutely love considering life as another expandable resource, I think your deck may be going a little too far this way. Unless I'm mistaken, you don't run any drain life, and a lot of self-inflicted pain. Flipping Tombstalker with Bob's help is going to kill you more often than not. You may want to include Sensei's Divining Top to help with library manipulation if Bob is your main draw engine, or the mana curve of your deck will prove lethal.

Apart from Tombstalker, your critters aren't especially resilient (pumpers like Nantuko can't always be large, Bob is 2/1 and Hippie is a Lightning catcher), and you only run 1 for 1 removal. So that spells trouble against decks packing efficient creatures.

Your mana base is also a little sketchy, running only 19 lands, one Sol Ring, and 5 one-shot mana sources. Strip Mine is a nice card, but you should probably complement it with some Wastelands. You could also include some Creature-lands, which are uncounterable (control hates that), and are harder to steal/sweep.

Also, discard can be a potent disruption strategy (duress, thoughtsiege), but it is far from an ideal win condition nowadays.
- a fast aggro deck will have his hand empty and threats on the board that will eat your utility critters for breakfast before you know it
- a single topdecked "Draw 7" can leave you up the proverbial creek without a paddle
- against combo, filling his graveyard can mean Game Over if he draws either Yagwmoth or a Tutor to Yagwmoth
- once your opponent is in topdeck mode, your discard isn't very useful (although Hippie can still hit for 2 each turn)

You should really replace Night's Whisper by Sign in Blood, which is more versatile as it can target the opponent in case you just need those extra couple damage points.

So to sum it up :
- fix your mana base
- improve your draw engine, either including library manipulation, or switching to something else like Necropotence + Drain Life (oldies but goodies)
- change your win conditions, as running "utility" critters and discard/Rack may not be enough, even in a control-heavy meta, where there will always be a counter/disenchant for your Racks. In 2010, Sanguine Bond coupled with lifelink critters or drain-life effects is a pretty good win condition for mono-black. Liliana Vess is another recent card you could consider, as it has some good synergy with your discard deck.
- better critters (it looks like you are in luck with Zendikar incoming, as there seem to be a lot of extremely efficient black creatures in it)
- additional removal : the problem with discard is just like countermagic : once you let a threat hit the table (hard to prevent with discard unless you completely strip their lands T1), then you have a potential problem on your hand. The problem is made worse by Cascade spells, with which discard can't cope well (since a single cascaded spell can result in several new threats to deal with). Your deck could use a couple sweepers (black Wrath, Nevinyrral's Disk)

Hope this helps,