I have a TON of fun with Marksman and Sneak skills.
Get this, with standard Marksman skill at say level 50, you can do 3x the damage if you strike a creature while in Sneak mode undetected.
You can also use Alchemy to create powerful poisons to add to the damage, and bows can be enchanted, I usually stick with Sigil Stones to keep in character.
Marksman in vanilla Oblivion is rather weak though, I use the "Eagle Eye" Realistic Archery Mod to make archery more fun. Todd Howard has recently come out saying that it was mods just like this that made them take a different approach at how Marksmen was implemented in Skyrim.
The best part though is simply spotting a baddie some 100 or more feet out down a dark corridor, knocking a poisoned arrow, zooming in for accuracy (Marksmen Perk), and either knocking the baddie down (Marksman Perk) or out-right killing it, knocking it 10 feet back in the process.
It gets even more fun when you realize you were never spotted, and you can simply repeat that process with as many baddies as you can before they spot you.
Peace,
Dan O.