Let see... I have 1 dead laptop (5yrs ago), 1 dead tablet PC (3 yrs ago), 1 tablet pc (1 yr ago) - I tend to not spend more than $1000 at a time, so $500/year on laptops.
Oh yeah, got 2 EEE PC 4Gs when they first came out with SDHC cards and a few other extras - so that was about almost $1000.
I have enough parts at home for at least 5 PCs, but only 3 are up and active. I usually buy a decent all-in-one motherboard ($100-150). RAM upgrades are usually around $75 each round. (I have 8GB in a server, 8GB in a Vista machine, and 2 GB in an XP machine right now... and probably 2-4GB sitting around.) Haven't bought a dedicated sound card in quite a while, and I occasionally buy a video card for $75ish. Hard drives I rarely spend more than $100 for. CD Drives I'll spend around $40 tops, but I did spend $200 on a blu-ray burner. Cases I try to keep under $100 and usually with a power supply, but I'll occasionally drop $50 to $100 for a decent and energy efficient power supply. Go for CPUs under $100 usually, so that typically means AMD. OEM software as needed - $140 on average (which is why I am thinking about going Linux mainly + VMWare player and 1 copy of workstation... but keeping one native windows machine).
So how much do I spend on a system? I don't really know. For laptops, $500-$1000 per year sounds right for an average - but for desktops, I use the "upgrade with a couple of hundred bucks" every 3-6 months. So I really don't know how much I've invested in technology total, or even per year - a lot, but a lot less than the cooks at Denny's seem to sink into customizing their rides.
Guess I'll have to start a log of my computer expenses!