There's a good thread about latency and VPS.

Dealing latency with ZenFire & NT I live in NZ and have been trading on SIM via AMP Futures in Chicago. At this stage I am focusing on the FESX out of Europe. What I can't test under SIM is what sort of delay there is in me receiving the exchange data in NZ and equally what delay …

Like Matt already mentioned, trading is getting faster and faster and therefore, every daytrader should worry about latency. But for sure, scalpers should worry more about latency than traders who use a 15min chart.

Let me give you an example, how even non-scalpers can benefit from using a virtual trading workstation. Let's say you have an open position in 6E and you are using a trailing stop to secure your profits. When the market is turning against you, you need instant execution to secure your profits. Proximity Hosting dramatically increases your chance to get filled on the price your trailing stop sits at. Even if you just lose just1 pip per trade because of bad execution from home and you're doing 10 trades per day, that sums up to 125$ per day, 2.500$ per month....

Despite the faster execution, you also get the benefits BigMike has mentioned. Never underestimate the value of a trading workstation running smoothly 24/7 without any errors or downtime. It lets you sleep well!

If latency for you is an issue you should look at ZenFire.

GuerillaTrading 

Even if you just lose just1 pip per trade because of bad execution from home and you're doing 10 trades per day, that sums up to 125$ per day, 2.500$ per month....

I agree that once you quantify it you can really see the difference that latency could make.