I would like to start mining, but my GPU isn't the greatest and I don't really want to spend the money on a dedicated rig. Is mining from my CPU (in a Linux environment) still worth it? Or will I not be able to keep up?
For the amount of time you would spend setting up a CPU miner, at minimum wage in the US you would be at a loss.
Even GPU mining is barely profitable for most people right now. It would definitely be more profitable to speculate, and even more profitable to operate a Bitcoin business. There are a great deal of people who want to use their Bitcoins for purchases.
At the current exchange of under $10:1BTC, the most efficient graphics cards are taking months to pay off their initial investment (with free electricity).
It depends on your specific valuation of "worth it."
By most valuations (i.e. value of BTC produced > electricity costs) it is not, but if you don't pay for electricity it might be. It might also be worth it to you to mine at a loss if you truly believe that 1 BTC might be worth thousands someday.
Realistically, though, it is probably more worthwhile to simply purchase BTC at an exchange or from another user.
I'm in a mining pool, using several multi-core servers and generating about 7-10Mhashes/second. It has yielded me currently about $0.01 dollars in the last 36 hours. I do not pay for electricity. I made a penny. It's not that exciting. :) There are GPUs that can accumulate my MHash rate that I create across several CPUs, without even getting warm. So my guess, based on my experience, is "no"
CPU mining is only worth it if you are not paying for your electricity.
The forks Tenebrix and Fairbrix are designed to give an advantage to CPUs. It might be more profitable to CPU mine them than Bitcoin or other GPU-algorithm forks.
All the mining pools I tried required you to have .01 BTC in credits before withdrawing. With a CPU at the current rate, this could easily take a year to reach. And as the difficulty continues to rise, there's a large chance that you would never reach this .01 BTC threshold. So unless you're doing something like operating a botnet, the answer is "no". And even with a botnet, there are more profitable things you could be doing.
That said, do tell me if you happen to find a pool that has a smaller (or no) payment threshold.
use this calculator http://www.coinish.com/calc/ I think it will answer your question perfectly use 'expert' mode for most accurate results (never 100% correct, that's impossible)