Homegrown hops can be successfully used for bittering and can have the same "effect" as commercial grown hops provide you do everything correctly.
The first problem is that the typical homegrower harvests way too early. They look at the big, green cone and think "how beautiful". They can't wait to get it into a beer. The reality is that the alpha acids (bittering compounds) are some of the last things to develop in the cone. So if the cones are picked early, the oils and aroma may be there but the bittering isn't. When some of our growers jump the gun and harvest a week or two early, we see alpha's drop from an expected 6% to something like 1% for example. That little bit of time really matters.
The second problem is that home growers don't always dry to the same level as commercial growers. Commercial growers have to get below 12% to pelletize and most shoot for 10% or less. Most home grown stuff I have sampled is still in the 15 to 20% range or more. This doesn't sound like much but a 4 oz sample dried to 10% contains 0.4 oz water. A 4 oz sample dried to 20% contains .8 oz of water. In other words, if your recipe called for 4 oz of hops for bittering and you used 4 oz of the 20% moisture content hops, you would be getting 12% less alpha than the 10% moisture content hops your recipe assumes you are using. Make sense?
The final problem is in water/fertilizer application and weather. I'm amazed at how drastically hop chemistry can be effected by small changes in their growing conditions.
I like allynlyon's suggestion of making a hop tea to see if the bittering potential is there before you use it to brew. That may save you from having to dump a future batch.
