Elad Gil posted an excellent analysis yesterday, following on from Chris Dixon's post in March, on VC signaling regarding seed-round investments. He mentions 'bridge financing' (such as a RevenueLoan from Lighter Capital) as an alternative that eliminates the equity follow-on signalling issue altogether.
Here's the 140 character summary (give or take): A VC seed round investment is great for them. They can make 100 $100k bets for 2% of their portfolio (~$500MM) and then have more information on those companies than the rest of the market when it comes time for the Series A. That same investment feels good to the company because they get a TechCrunch article, what have you, touting how a top tier VC invested in their company. But when they go to raise their true Series A and that top tier VC isn't re-upping, it sends a very negative signal to the rest of the market.
My advice: resist, resist, resist that VC fan-boy urge! Bootstrap ("Your cap table is only clean once!"), borrow from friends and family, or secure non-dilutive growth/bridge financing like revenue-based finance.
And Chris Dixon's post: http://cdixon.org/2010/03/11/the-importance-of-investor-signaling-in-venture-pricing/