I'm trying to summarize here. I Googled this topic and found bits and pieces about how to do it, but not all together at once.
Original Q & A:
Q: "I have system restore set with an unbound upper limit, is this going to cause any problems later?"
A: "It depends on whether you need the hard drive space that you set for it as it fills up. As the space you set fills up, older restore points will automatically be deleted to make room for the new ones, so you shouldn't have a problem at all."
Now, as for viewing or changing the allocated HD space for System Restore Points, the only thing I can find is doing it via command prompt.
I won't go into what the command prompt is or anything because anybody who is worried about the size of System Restore Points probably knows their way around the command prompt and the Registry as well.
Anyway, to sum it up:
At the command prompt (Admin), to see the currently allocated space type: vssadmin list ShadowStorage
C:\Windows\System32>vssadmin list ShadowStorage
You will get an output like this:
Used Shadow Copy Storage space: 1.291GB
Allocated Shadow Copy Storage space: 1.563GB
Maximum Shadow Copy Storage space: 11.25GB
Sizes you see listed as well as sizes you can enter are in KB, MB, GB, TB, and up.
As you can see, 1.29GB is currently in use on my system.
To change the amount of used HD space: (increase or decrease)
vssadmin Resize /For=C: /On=C: /MaxSize=4GB
Change the drive letters to what you want (my guess is that we're mostly all talking about C: here, though.)
For "/MaxSize=", change it to what you want.
As a side note, some users complain that they notice available disk space disappearing, though System Restore was disabled for one, some, or all drives present.
The fix was to use vssadmin for all drives in your system.
For example, for drive C:, set it for what you want, and as my system for example, set S: and Z: to 10MB.
That way things on non-system drives won't get out of hand.
This may not apply to you. Personally, I never experienced this problem, however, some people have complained about it and this is how to fix it.
Also, note that (I won't get into all that here) Volume Shadow Copy Service (VSS) stores more than System Restore Points, so the idea is to set it at a reasonable size.