Teabags are not the perfect tea delivery mechanisms. In the first place, I have yet to see a teabag that allows the tea contained inside to spread out as much as it ought to spread out during the brewing process. During brewing, tea is rehydrated, and it can expand to three or four times is dry volume. There simply isn't enough room in a teabag to accommodate that degree of expansion, and that inhibits the infusion of the hot water with all of the tea-y goodness. Secondly, top-quality tea rarely goes into teabags. You're not going to find whole-leaf teas in bags, and it's likely that there will be a non-trivial quantity of finings in the blend. The word "finings" is just a nice euphemism for tea dust, and the more tea dust and tiny tea pieces in the bag, the more bitterness the brew will have.
Still, anyone who likes tea sooner or later will have to reconcile himself to using teabags sometimes. Restaurants that serve loose tea are few and far between, and there are places (such as the office) where it isn't practical to have the full loose tea-brewing rig. If you're going to use teabags sometimes, you ought to spend the extra money to get teabags produced by quality vendors. The Republic of Tea and Harney & Sons are two such. Their bags are large, not overstuffed, and are made from unbleached paper (well, Republic of Tea's certainly are; I'm not sure about Harney & Sons) to reduce off flavors. And the tea that goes in the bags doesn't contain many finings. I'd still rather have loose tea, of course, but I can get by with bags such as these when necessary.