This may depend on how the question of the 1 MB max blocksize limit is handled. One thing is certain without an increase in this limit, and a hark fork is necessary for this, Bitcoin will be dethroned by a competitor. Once the limit is reached transaction fees will skyrocket as an ever growing number of transactions compete for the 1 MB space every 10 min. Fortunately Gavin Andresen understands the need for this. So do other Bitcoin developers. The real question in my mind is will they muster the necessary community consensus to make this hard fork happen?
In the absence of a hard fork, how soon do we expect to hit this limit?
I have heard estimates in the range of one year. What I would recommend, however, is to spend some time at https://blockchain.info/ and take a look at what is actually happening in the Bitcoin network in real time and then form one's own opinion, rather than depend on what I or someone else may say.
Many people cite 7 transactions per second (tps) as the limit for 1 MB blocks, but 3 tps is probably more accurate.
Here's a chart that uses extrapolation to estimate the dates when the bitcoin network would reach the blocksize limit (3 tps or 7 tps) if historical growth rates hold. If we witness another "growth spurt," I expect we will approach 3 tps on several days and the discussions with regards to increasing the blocksize will become more focussed.
