I've played several systems that used that sort of resolution mechanic (Marvel Heroic, Dogs in the Vineyard, some Savage Worlds). I like resolution systems that lets you build fiction in a scene and grow your pool/roll/bonuses as you do so. Fate does this same thing only in a different way, and I love Fate. The only mathematical issues we've come across is when the dice pool system has exploding die. Smaller dice have a much higher chance of rolling a "critical" (e.g. a 4 on a D4 or a 20 on a D20) than larger dice do, so in certain situations my players would sandbag, rolling a smaller die, to increase their chance of a critical. It made for some interesting stories, so I kinda liked it. But it came out a bit weird mathematically sometimes. :-)