approx. how many miles should i go before replacing my chain? i bought the bike new in may and just crossed the 2000 mile mark. not a lot of hard riding. mostly commuting with a few weekend warrior treks. three or four 10 mile TT's for fun.

The general wisdom, if you're just going to replace chains sequentially in hopes of making the cassette last longer, is to replace the chain when 12 full links measure 12-1/16" long. Or when your chain checking tool of choice tells you to. This is a hotly-debated topic, so brace yourself.

Measuring chain wear is the only way to know, at least until you get a sense of your riding style over a long time. Rider weight, terrains, rain and other bad weather conditions, how much your sprint, how hard and often you climb, cadence, and many other things affect waer.

+1

Yes, despite the prediction, there's no debate so far.

You can't use averages because chain life varies so much person to person, running from a low of less than 1,000 miles to a claimed 18,000. use a ruler and follow the general guideline of replacing at 1/2% stretch (1/16" over 12"). Since this is only a rough guideline and you're eyeballing the measurement, no great amount of precision is called for.